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Exponential integrals, and related functions
===============================================================================





Exponential integral `E_1(x)`
-------------------------------------------------------------------------------

.. method:: ctx.exp_integral_e1(x)

    where ``ctx`` is ``math53`` or ``ctxflint``.

    Returns the exponential integral `\displaystyle E_1(x) =  \int_1^\infty \frac{e^{-xt}}{t} \, \mathrm{d}t, = e^{-z} U(1,1,z), \quad x \neq 0`. 


    For real `x<0` the integral can be calculated as `E_1(x) = -\mathrm{Ei}(-x)`. 

    See also   Wikipedia :cite:p:`WikipediaFun175`, MathWorld :cite:p:`WolframFun175`, NIST :cite:p:`DLMFun175`,  BoostMath :cite:p:`BoostFun175`, :cite:t:`Ehrhardt2018` (3.4.5), :cite:t:`Ehrhardt2018` (4.2.27), Flint :cite:p:`FlintFun175`, Flint :cite:p:`FlintFun176`, Mpmath :cite:p:`MpmathFun175`. 





    An example in Python

    .. code-block:: pycon

        >>> from xlcalcnet import ereal
        >>> ereal.E1(0.5)
        ereal('5.2359877559829887307E-1')
        >>> ereal.E1('0.51')
        ereal('5.3518479027559984754E-1')




    An example with real input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 40; x = 3.0
        >>> \mathrm{d}x = dec.e1(x); mx = mpm.e1(x); gx = gmp.e1(x)
        >>> fx = fpm.e1(x); ax = apm.e1(x)
        >>> mpm.show([\mathrm{d}x, mx, gx, fx, ax])
        dec:  1.304838109419703741250074582864502294848E-2
        mpm:  1.304838109419703741250074582864502294848e-2
        gmp:  1.304838109419703741250074582864502294848E-02
        fpm:  1.30483810941970E-02
        apm:  1.304838109419703741250074582864502294848e-2 (8.248e-39%)


    An example with complex input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 20; z = '3.0 + 4.0j'
        >>> \mathrm{d}z = dec.e1(z); mz = mpm.e1(z); gz = gmp.e1(z)
        >>> fz = fpm.e1(z); az = apm.e1(z)
        >>> mpm.show([\mathrm{d}z, mz, gz, fz, az], aligned=True)
        dec: 8.6395395897958511158E-4              + 8.7862083771974420418E-3j
        mpm: 8.6395395897958511158e-4              + 8.7862083771974420418e-3j
        gmp: 8.6395395897958511158E-04             + 8.7862083771974420418E-03j
        fpm: 8.63953958979585E-04                  + 8.78620837719744E-03j
        apm: 8.6395395897958511148e-4 (8.234e-17%) + 8.7862083771974420418e-3 (7.381e-18%)j






|newpage|

Exponential integral `\mathrm{Ei}(x)`
-------------------------------------------------------------------------------

.. method:: ctx.exp_integral_ei(x)

    where ``ctx`` is ``math53``, ``mathc53``, ``ctxboost`` or ``ctxflint``.

    Returns the exponential integral  `\displaystyle  \mathrm{Ei}(x) = -PV \int_{-x}^\infty \frac{e^{-t}}{t} \, \mathrm{d}t= PV \int_{-\infty}^x \frac{e^{t}}{t} \, \mathrm{d}t`. 
    
    For real `x<0` we have `\mathrm{Ei}(x) = -E_1(-x)`. 

    See also   Wikipedia :cite:p:`WikipediaFun175`, MathWorld :cite:p:`WolframFun175`, NIST :cite:p:`DLMFun175`,  BoostMath :cite:p:`BoostFun175`, :cite:t:`Ehrhardt2018` (3.4.7), :cite:t:`Ehrhardt2018` (4.2.27), Flint :cite:p:`FlintFun175`, Flint :cite:p:`FlintFun176`, Mpmath :cite:p:`MpmathFun176`. 



    The exponential integral `\mathrm{Ei}(z)` can also be calculated as
    using

    .. math ::

        \mathrm{Ei}(z) = -e^z U(1,1,-z) - \log(-z)
            + \frac{1}{2} \left(\log(z) - \log\left(\frac{1}{z}\right) \right)





    |06a_TestEi_re| `\quad` |06b_TestEi_im| `\quad` |06c_TestEi_abs|

    .. |06a_TestEi_re| image:: ../_static/ExplicitSurfaces/Cplx1F1/06a_TestEi_re.3D.xml.jpg
       :width: 30 %

    .. |06b_TestEi_im| image:: ../_static/ExplicitSurfaces/Cplx1F1/06b_TestEi_im.3D.xml.jpg
       :width: 30 %

    .. |06c_TestEi_abs| image:: ../_static/ExplicitSurfaces/Cplx1F1/06c_TestEi_abs.3D.xml.jpg
       :width: 30 %

       

    **3D wpf plot**: real part (left figure), imaginary part (middle figure) and absolute value with color-coded phase (right figure) of the complex sine function `z = \sin(x + iy)`, with `-6 \le x \le 6` (blue axis), `-6 \le y \le 6` (red axis), `-10 \le z \le 10` (green axis). Function values are :ref:`loglog-transformed <rst_mpm_loglog_transformation>`.








    An example in Python

    .. code-block:: pycon

        >>> from xlcalcnet import ereal
        >>> ereal.Ei(0.5)
        ereal('5.2359877559829887307E-1')
        >>> ereal.Ei('0.51')
        ereal('5.3518479027559984754E-1')




    An example with real input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 40; x = 3.0
        >>> \mathrm{d}x = dec.ei(x); mx = mpm.ei(x); gx = gmp.ei(x)
        >>> fx = fpm.ei(x); ax = apm.ei(x)
        >>> mpm.show([\mathrm{d}x, mx, gx, fx, ax])
        dec:  9.933832570625416558008336019216765262991E+0
        mpm:  9.933832570625416558008336019216765262991e+0
        gmp:  9.933832570625416558008336019216765262991E+00
        fpm:  9.93383257062542E+00
        apm:  9.933832570625416558008336019216765262991e+0 (9.245e-40%)


    An example with complex input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 20; z = '3.0 + 4.0j'
        >>> \mathrm{d}z = dec.ei(z); mz = mpm.ei(z); gz = gmp.ei(z)
        >>> fz = fpm.ei(z); az = apm.ei(z)
        >>> mpm.show([\mathrm{d}z, mz, gz, fz, az], aligned=True)
        dec: -4.1540916516426898225E+0               + 4.2944186200243574770E+0j
        mpm: -4.1540916516426898225e+0               + 4.2944186200243574770e+0j
        gmp: -4.1540916516426898225E+00              + 4.2944186200243574770E+00j
        fpm: -4.15409165164269E+00                   + 4.29441862002436E+00j
        apm: -4.1540916516426898225e+0 (-8.156e-20%) + 4.2944186200243574770e+0 (7.89e-20%)j


        


|newpage|

Logarithmic integral `\mathrm{li}(x)`
-------------------------------------------------------------------------------

.. method:: ctx.log_integral(z)

    where ``ctx`` is ``math53``, ``mathc53`` or ``ctxflint``.

    Returns the logarithmic integral `\displaystyle \mathrm{li}(x) = PV \int_{0}^{x} \frac{1}{\log(t)} \, \mathrm{d}t, \quad (x \geq 0, x \neq 1)`. 
    
    For `x \neq 0` the integral is calculated as `\mathrm{li}(x)=\mathrm{Ei}(\log(x))`. 

    See also   Wikipedia :cite:p:`WikipediaFun177`, MathWorld :cite:p:`WolframFun177`, NIST :cite:p:`DLMFun177`, :cite:t:`Ehrhardt2018` (3.4.15), :cite:t:`Ehrhardt2018` (4.2.40), Flint :cite:p:`FlintFun175`, Flint :cite:p:`FlintFun176`, Mpmath :cite:p:`MpmathFun177`. 




    |07a_TestLi_re| `\quad` |07b_TestLi_im| `\quad` |07c_TestLi_abs|

    .. |07a_TestLi_re| image:: ../_static/ExplicitSurfaces/Cplx1F1/07a_TestLi_re.3D.xml.jpg
       :width: 30 %

    .. |07b_TestLi_im| image:: ../_static/ExplicitSurfaces/Cplx1F1/07b_TestLi_im.3D.xml.jpg
       :width: 30 %

    .. |07c_TestLi_abs| image:: ../_static/ExplicitSurfaces/Cplx1F1/07c_TestLi_abs.3D.xml.jpg
       :width: 30 %

       

    **3D wpf plot**: real part (left figure), imaginary part (middle figure) and absolute value with color-coded phase (right figure) of the complex sine function `z = \sin(x + iy)`, with `-6 \le x \le 6` (blue axis), `-6 \le y \le 6` (red axis), `-10 \le z \le 10` (green axis). Function values are :ref:`loglog-transformed <rst_mpm_loglog_transformation>`.






    An example in Python

    .. code-block:: pycon

        >>> from xlcalcnet import ereal
        >>> ereal.Li(0.5)
        ereal('5.2359877559829887307E-1')
        >>> ereal.Li('0.51')
        ereal('5.3518479027559984754E-1')




    An example with real input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 40; x = 3.0
        >>> \mathrm{d}x = dec.li(x); mx = mpm.li(x); gx = gmp.li(x)
        >>> fx = fpm.li(x); ax = apm.li(x)
        >>> mpm.show([\mathrm{d}x, mx, gx, fx, ax])
        dec:  2.163588594667191972876922367347721366542E+0
        mpm:  2.163588594667191972876922367347721366542e+0
        gmp:  2.163588594667191972876922367347721366542E+00
        fpm:  2.16358859466719E+00
        apm:  2.163588594667191972876922367347721366542e+0 (1.061e-39%)


    An example with complex input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 20; z = '3.0 + 4.0j'
        >>> \mathrm{d}z = dec.li(z); mz = mpm.li(z); gz = gmp.li(z)
        >>> fz = fpm.li(z); az = apm.li(z)
        >>> mpm.show([\mathrm{d}z, mz, gz, fz, az], aligned=True)
        dec: 3.1343755504645775265E+0              + 2.6769247817778742392E+0j
        mpm: 3.1343755504645775265e+0              + 2.6769247817778742392e+0j
        gmp: 3.1343755504645775265E+00             + 2.6769247817778742392E+00j
        fpm: 3.13437555046458E+00                  + 2.67692478177787E+00j
        apm: 3.1343755504645775265e+0 (1.081e-19%) + 2.6769247817778742392e+0 (6.328e-20%)j











|newpage|

Hyperbolic sine integral `\mathrm{Shi}(x)`
-------------------------------------------------------------------------------

.. method:: ctx.sinh_integral(x)

    where ``ctx`` is ``math53``, ``ctxflint``.

    Returns the hyperbolic sine integral `\displaystyle \mathrm{Shi}(x) =  \int_0^x \frac{\sinh(t)}{t} \, \mathrm{d}t`. 

    See also   Wikipedia :cite:p:`WikipediaFun181`, MathWorld :cite:p:`WolframFun181`, NIST :cite:p:`DLMFun180`, :cite:t:`Ehrhardt2018` (3.4.17), Flint :cite:p:`FlintFun175`, Flint :cite:p:`FlintFun176`, Mpmath :cite:p:`MpmathFun181`. 

    For real `x` the integral is calculated using the relations `\displaystyle  \text{Shi}(x) = \tfrac{1}{2} \left(\text{Ei}(x)+\text{E}_1(x)\right)` for `x>0` and  `\mathrm{Shi}(x) = -\mathrm{Shi}(-x)` for `x<0`.

    For complex  `x` the integral is calculated using the relation `\displaystyle  \text{Shi}(x) = -i \text{Si}(ix)`. 



    An example in Python

    .. code-block:: pycon

        >>> from xlcalcnet import ereal
        >>> ereal.Shi(0.5)
        ereal('5.2359877559829887307E-1')
        >>> ereal.Shi('0.51')
        ereal('5.3518479027559984754E-1')




    An example with real input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 40; x = 3.0
        >>> \mathrm{d}x = dec.shi(x); mx = mpm.shi(x); gx = gmp.shi(x)
        >>> fx = fpm.shi(x); ax = apm.shi(x)
        >>> mpm.show([\mathrm{d}x, mx, gx, fx, ax])
        dec:  4.973440475859806797710418382522705142970E+0
        mpm:  4.973440475859806797710418382522705142970e+0
        gmp:  4.973440475859806797710418382522705142970E+00
        fpm:  4.97344047585981E+00
        apm:  4.973440475859806797710418382522705142970e+0 (9.233e-40%)


    An example with complex input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 20; z = '3.0 + 4.0j'
        >>> \mathrm{d}z = dec.shi(z); mz = mpm.shi(z); gz = gmp.shi(z)
        >>> fz = fpm.shi(z); az = apm.shi(z)
        >>> mpm.show([\mathrm{d}z, mz, gz, fz, az], aligned=True)
        dec: -2.0766138488418551187E+0               + 2.1516024142007774595E+0j
        mpm: -2.0766138488418551187e+0               + 2.1516024142007774595e+0j
        gmp: -2.0766138488418551187E+00              + 2.1516024142007774595E+00j
        fpm: -2.07661384884186E+00                   + 2.15160241420078E+00j
        apm: -2.0766138488418551187e+0 (-1.632e-19%) + 2.1516024142007774595e+0 (7.874e-20%)j





|newpage|

Hyperbolic cosine integral `\mathrm{Chi}(x)`
-------------------------------------------------------------------------------

.. method:: ctx.cosh_integral(x)

    where ``ctx`` is ``math53``, ``ctxflint``.

    Note: Also math53.chi(z), ctx.coshIntegral(z)

    Returns the hyperbolic cosine integral `\displaystyle \mathrm{Chi}(x) = -\int_x^{\infty} \frac{\cosh(t)}{t} \, \mathrm{d}t = \gamma + \log(x) + \int_0^x \frac{\cosh(t) - 1}{t} \, \mathrm{d}t`.

    See also   Wikipedia :cite:p:`WikipediaFun180`, MathWorld :cite:p:`WolframFun180`, NIST :cite:p:`DLMFun180`, :cite:t:`Ehrhardt2018` (3.4.1), Flint :cite:p:`FlintFun175`, Flint :cite:p:`FlintFun176`, Mpmath :cite:p:`MpmathFun180`. 



    For real `x` the integral is calculated using the relations `\displaystyle  \text{Chi}(x) = \tfrac{1}{2} \left(\text{Ei}(x)-\text{E}_1(x)\right)` for `x>0` and `\text{Chi}(x) = \text{Chi}(-x)` for `x<0`.

    For complex  `x` the integral is calculated using the relation `\displaystyle \text{Chi}(x) = \text{Ci}(i x) - \log(i x) + \log(x)`. 





    An example in Python

    .. code-block:: pycon

        >>> from xlcalcnet import ereal
        >>> ereal.Chi(0.5)
        ereal('5.2359877559829887307E-1')
        >>> ereal.Chi('0.51')
        ereal('5.3518479027559984754E-1')




    An example with real input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 40; x = 3.0
        >>> \mathrm{d}x = dec.chi(x); mx = mpm.chi(x); gx = gmp.chi(x)
        >>> fx = fpm.chi(x); ax = apm.chi(x)
        >>> mpm.show([\mathrm{d}x, mx, gx, fx, ax])
        dec:  4.960392094765609760297917636694060120021E+0
        mpm:  4.960392094765609760297917636694060120021e+0
        gmp:  4.960392094765609760297917636694060120021E+00
        fpm:  4.96039209476561E+00
        apm:  4.960392094765609760297917636694060120020e+0 (6.387e-38%)


    An example with complex input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 20; z = '3.0 + 4.0j'
        >>> \mathrm{d}z = dec.chi(z); mz = mpm.chi(z); gz = gmp.chi(z)
        >>> fz = fpm.chi(z); az = apm.chi(z)
        >>> mpm.show([\mathrm{d}z, mz, gz, fz, az], aligned=True)
        dec: -2.0774778028008347038E+0               + 2.1428162058235800175E+0j
        mpm: -2.0774778028008347038e+0               + 2.1428162058235800175e+0j
        gmp: -2.0774778028008347038E+00              + 2.1428162058235800175E+00j
        fpm: -2.07747780280083E+00                   + 2.14281620582358E+00j
        apm: -2.0774778028008347038e+0 (-1.631e-19%) + 2.1428162058235800175e+0 (1.581e-19%)j









|newpage|

Generalized exponential integral `E_n(x)`
-------------------------------------------------------------------------------

.. method:: ctx.exp_integral_en(n, z)

    where ``ctx`` is ``math53``, ``ctxboost`` or ``ctxflint``.


    Returns the generalized exponential integral of integer order `\displaystyle E_n(x) = \int_{1}^{\infty} \frac{e^{-xt}}{t^n} \, \mathrm{d}t, \quad (n \geq 0)`.

    See also   Wikipedia :cite:p:`WikipediaFun175`, MathWorld :cite:p:`WolframFun176`, NIST :cite:p:`DLMFun176`,  BoostMath :cite:p:`BoostFun176`, :cite:t:`Ehrhardt2018` (3.4.12), Mpmath :cite:p:`MpmathFun176a`. 

    The function can be generalized for complex `s` and complex `z` using

    .. math :: \text{E}_{1-s}(z) = z^{-s} \Gamma(s,z).


    An example in Python

    .. code-block:: pycon

        >>> from xlcalcnet import ereal
        >>> ereal.En(3, 0.5)
        ereal('5.2359877559829887307E-1')
        >>> ereal.En(3, '0.51')
        ereal('5.3518479027559984754E-1')





    An example with real input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 40; n = '4'; x = '5.0'
        >>> \mathrm{d}x = dec.expint(n, x); mx = mpm.expint(n, x); gx = gmp.expint(n, x)
        >>> fx = fpm.expint(n, x); ax = apm.expint(n, x)
        >>> mpm.show([\mathrm{d}x, mx, gx, fx, ax])
        dec:  7.829808450774252432788031803000123235715E-4
        mpm:  7.829808450774252432788031803000123235715e-4
        gmp:  7.829808450774252432788031803000123235715E-04
        fpm:  7.82980845077425E-04
        apm:  7.829808450774252432788031803000123235723e-4 (2.172e-36%)


    An example with complex input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 20; n = '4'; z = '5.0 + 3.0j'
        >>> \mathrm{d}z = dec.expint(n, z); mz = mpm.expint(n, z); gz = gmp.expint(n, z)
        >>> fz = fpm.expint(n, z); az = apm.expint(n, z)
        >>> mpm.show([\mathrm{d}z, mz, gz, fz, az], aligned=True)
        dec: -7.1820162264651649511E-4               + 1.4860820449934938829E-4j
        mpm: -7.1820162264651649511e-4               + 1.4860820449934938829e-4j
        gmp: -7.1820162264651649511E-04              + 1.4860820449934938829E-04j
        fpm: -7.18201622646517E-04                   + 1.48608204499349E-04j
        apm: -7.1820162264651649571e-4 (-1.103e-15%) + 1.4860820449934939066e-4 (8.075e-15%)j







|newpage|

Sine integral `\mathrm{Si}(x)`
-------------------------------------------------------------------------------

.. method:: ctx.sin_integral(z)

    where ``ctx`` is ``math53``, ``ctxflint``.


    Returns the sine integral `\displaystyle \mathrm{Si}(x) =  \int_0^x \frac{\sin(t)}{t} \, \mathrm{d}t`, and `\mathrm{Si}(x) = -\mathrm{Si}(-x)` for `x<0`.

    See also   Wikipedia :cite:p:`WikipediaFun179`, MathWorld :cite:p:`WolframFun179`, NIST :cite:p:`DLMFun178`, :cite:t:`Ehrhardt2018` (3.4.18), Flint :cite:p:`FlintFun175`, Flint :cite:p:`FlintFun176`, Mpmath :cite:p:`MpmathFun179`.


    For complex `z`, the sine integral `\mathrm{Si}(z)` can be computed using

    .. math ::

        \mathrm{Si}(z) = \frac{i}{2} \left[
            e^{iz} U(1,1,-iz) - e^{-iz} U(1,1,iz) + 
            \log(-iz) - \log(iz) \right]

    .. math ::

        \mathrm{Si}(z) = z {}_1F_2(\tfrac{1}{2}; \tfrac{3}{2}, \tfrac{3}{2}; -\tfrac{z^2}{4})

    and an automatic algorithm choice.





    |13a_TestSinIntegral_re| `\quad` |13b_TestSinIntegral_im| `\quad` |13c_TestSinIntegral_abs|

    .. |13a_TestSinIntegral_re| image:: ../_static/ExplicitSurfaces/Cplx1F1/13a_TestSinIntegral_re.3D.xml.jpg
       :width: 30 %

    .. |13b_TestSinIntegral_im| image:: ../_static/ExplicitSurfaces/Cplx1F1/13b_TestSinIntegral_im.3D.xml.jpg
       :width: 30 %

    .. |13c_TestSinIntegral_abs| image:: ../_static/ExplicitSurfaces/Cplx1F1/13c_TestSinIntegral_abs.3D.xml.jpg
       :width: 30 %

       

    **3D wpf plot**: real part (left figure), imaginary part (middle figure) and absolute value with color-coded phase (right figure) of the complex sine function `z = \sin(x + iy)`, with `-6 \le x \le 6` (blue axis), `-6 \le y \le 6` (red axis), `-10 \le z \le 10` (green axis). Function values are :ref:`loglog-transformed <rst_mpm_loglog_transformation>`.






    An example in Python

    .. code-block:: pycon

        >>> from xlcalcnet import ereal
        >>> ereal.Si(0.5)
        ereal('5.2359877559829887307E-1')
        >>> ereal.Si('0.51')
        ereal('5.3518479027559984754E-1')




    An example with real input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 40; x = 3.0
        >>> \mathrm{d}x = dec.si(x); mx = mpm.si(x); gx = gmp.si(x)
        >>> fx = fpm.si(x); ax = apm.si(x)
        >>> mpm.show([\mathrm{d}x, mx, gx, fx, ax])
        dec:  1.848652527999468256397730251111973245165E+0
        mpm:  1.848652527999468256397730251111973245165e+0
        gmp:  1.848652527999468256397730251111973245165E+00
        fpm:  1.84865252799947E+00
        apm:  1.848652527999468256397730251111973245165e+0 (6.21e-40%)


    An example with complex input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 20; z = '3.0 + 4.0j'
        >>> \mathrm{d}z = dec.si(z); mz = mpm.si(z); gz = gmp.si(z)
        >>> fz = fpm.si(z); az = apm.si(z)
        >>> mpm.show([\mathrm{d}z, mz, gz, fz, az], aligned=True)
        dec: 6.7479950814040320927E+0              - 3.4986637211319094706E+0j
        mpm: 6.7479950814040320927e+0              - 3.4986637211319094706e+0j
        gmp: 6.7479950814040320927E+00             - 3.4986637211319094706E+00j
        fpm: 6.74799508140403E+00                  - 3.49866372113191E+00j
        apm: 6.7479950814040320927e+0 (1.004e-19%) - 3.4986637211319094706e+0 (-4.842e-20%)j



        


|newpage|

Cosine integral `\mathrm{Ci}(x)`
-------------------------------------------------------------------------------

.. method:: ctx.cos_integral(z)

    where ``ctx`` is ``math53`` or ``ctxflint``.

    Returns the cosine integral `\displaystyle \mathrm{Ci}(x) = -\int_x^{\infty} \frac{\cos(t)}{t} \, \mathrm{d}t = \gamma + \log(x) + \int_0^x \frac{\cos(t) - 1}{t} \, \mathrm{d}t`, and `\text{Ci}(x) = \text{Ci}(-x)` for `x<0`.


    For complex `z`, the cosine integral `\mathrm{Ci}(z)`, can be computed using

    .. math ::

        \mathrm{Ci}(z) = \log(z) - \frac{1}{2} \left[
            e^{iz} U(1,1,-iz) + e^{-iz} U(1,1,iz) + 
            \log(-iz) + \log(iz) \right]


    See also   Wikipedia :cite:p:`WikipediaFun178`, MathWorld :cite:p:`WolframFun178`, NIST :cite:p:`DLMFun178`, :cite:t:`Ehrhardt2018` (3.4.2), Flint :cite:p:`FlintFun175`, Flint :cite:p:`FlintFun176`, Mpmath :cite:p:`MpmathFun178`.




    |12a_TestCosIntegral_re| `\quad` |12b_TestCosIntegral_im| `\quad` |12c_TestCosIntegral_abs|

    .. |12a_TestCosIntegral_re| image:: ../_static/ExplicitSurfaces/Cplx1F1/12a_TestCosIntegral_re.3D.xml.jpg
       :width: 30 %

    .. |12b_TestCosIntegral_im| image:: ../_static/ExplicitSurfaces/Cplx1F1/12b_TestCosIntegral_im.3D.xml.jpg
       :width: 30 %

    .. |12c_TestCosIntegral_abs| image:: ../_static/ExplicitSurfaces/Cplx1F1/12c_TestCosIntegral_abs.3D.xml.jpg
       :width: 30 %

       

    **3D wpf plot**: real part (left figure), imaginary part (middle figure) and absolute value with color-coded phase (right figure) of the complex sine function `z = \sin(x + iy)`, with `-6 \le x \le 6` (blue axis), `-6 \le y \le 6` (red axis), `-10 \le z \le 10` (green axis). Function values are :ref:`loglog-transformed <rst_mpm_loglog_transformation>`.






    An example in Python

    .. code-block:: pycon

        >>> from xlcalcnet import ereal
        >>> ereal.Ci(0.5)
        ereal('5.2359877559829887307E-1')
        >>> ereal.Ci('0.51')
        ereal('5.3518479027559984754E-1')





    An example with real input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 40; x = 3.0
        >>> \mathrm{d}x = dec.ci(x); mx = mpm.ci(x); gx = gmp.ci(x)
        >>> fx = fpm.ci(x); ax = apm.ci(x)
        >>> mpm.show([\mathrm{d}x, mx, gx, fx, ax])
        dec:  1.196297860080003276264722811766778505468E-1
        mpm:  1.196297860080003276264722811766778505468e-1
        gmp:  1.196297860080003276264722811766778505468E-01
        fpm:  1.19629786008000E-01
        apm:  1.196297860080003276264722811766778505468e-1 (1.799e-39%)


    An example with complex input:

    .. code-block:: pycon

        >>> from xlcalcnet import dec, mpm, gmp, fpm, apm
        >>> mpm.dps = 20; z = '3.0 + 4.0j'
        >>> \mathrm{d}z = dec.ci(z); mz = mpm.ci(z); gz = gmp.ci(z)
        >>> fz = fpm.ci(z); az = apm.ci(z)
        >>> mpm.show([\mathrm{d}z, mz, gz, fz, az], aligned=True)
        dec: -3.4957570339825683441E+0               - 5.1759052151768084089E+0j
        mpm: -3.4957570339825683441e+0               - 5.1759052151768084089e+0j
        gmp: -3.4957570339825683441E+00              - 5.1759052151768084089E+00j
        fpm: -3.49575703398257E+00                   - 5.17590521517681E+00j
        apm: -3.4957570339825683441e+0 (-9.692e-20%) - 5.1759052151768084089e+0 (-6.546e-20%)j