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scipy.integrate.

# dblquad

scipy.integrate.dblquad(func, a, b, gfun, hfun, args=(), epsabs=1.49e-08, epsrel=1.49e-08)

  Compute a double integral.

  Return the double (definite) integral of `func(y, x)` from `x = a..b` and `y = gfun(x)..hfun(x)`.

  Parameters:
    funccallable

      A Python function or method of at least two variables: y must be the first argument and x the second argument.

    a, bfloat

      The limits of integration in x: a < b

    gfuncallable or float

      The lower boundary curve in y which is a function taking a single floating point argument (x) and returning a floating point result or a float indicating a constant boundary curve.

    hfuncallable or float

      The upper boundary curve in y (same requirements as gfun).

    argssequence, optional

      Extra arguments to pass to func.

    epsabsfloat, optional

      Absolute tolerance passed directly to the inner 1-D quadrature integration. Default is 1.49e-8. `dblquad` tries to obtain an accuracy of `abs(i-result) <= max(epsabs, epsrel*abs(i))` where `i` = inner integral of `func(y, x)` from `gfun(x)` to `hfun(x)`, and `result` is the numerical approximation. See epsrel below.

    epsrelfloat, optional

      Relative tolerance of the inner 1-D integrals. Default is 1.49e-8. If `epsabs <= 0`, epsrel must be greater than both 5e-29 and `50 * (machine epsilon)`. See epsabs above.

  Returns:
    yfloat

      The resultant integral.

    abserrfloat

      An estimate of the error.

  See also

  `quad`

    single integral

  `tplquad`

    triple integral

  `nquad`

    N-dimensional integrals

  `fixed_quad`

    fixed-order Gaussian quadrature

  `simpson`

    integrator for sampled data

  `romb`

    integrator for sampled data

  `scipy.special`

    for coefficients and roots of orthogonal polynomials

  Notes

  For valid results, the integral must converge; behavior for divergent integrals is not guaranteed.

  Details of QUADPACK level routines

  `quad` calls routines from the FORTRAN library QUADPACK. This section provides details on the conditions for each routine to be called and a short description of each routine. For each level of integration, `qagse` is used for finite limits or `qagie` is used if either limit (or both!) are infinite. The following provides a short description from [1] for each routine.

  qagse

    is an integrator based on globally adaptive interval subdivision in connection with extrapolation, which will eliminate the effects of integrand singularities of several types. The integration is is performed using a 21-point Gauss-Kronrod quadrature within each subinterval.

  qagie

    handles integration over infinite intervals. The infinite range is mapped onto a finite interval and subsequently the same strategy as in `QAGS` is applied.

  References

  [1]

  Piessens, Robert; de Doncker-Kapenga, Elise; Überhuber, Christoph W.; Kahaner, David (1983). QUADPACK: A subroutine package for automatic integration. Springer-Verlag. ISBN 978-3-540-12553-2.

  Examples

  Compute the double integral of `x * y**2` over the box `x` ranging from 0 to 2 and `y` ranging from 0 to 1. That is, \(\int^{x=2}_{x=0} \int^{y=1}_{y=0} x y^2 \,dy \,dx\).

      >>> import numpy as np
      >>> from scipy import integrate
      >>> f = lambda y, x: x*y**2
      >>> integrate.dblquad(f, 0, 2, 0, 1)
          (0.6666666666666667, 7.401486830834377e-15)

  Calculate \(\int^{x=\pi/4}_{x=0} \int^{y=\cos(x)}_{y=\sin(x)} 1 \,dy \,dx\).

      >>> f = lambda y, x: 1
      >>> integrate.dblquad(f, 0, np.pi/4, np.sin, np.cos)
          (0.41421356237309503, 1.1083280054755938e-14)

  Calculate \(\int^{x=1}_{x=0} \int^{y=2-x}_{y=x} a x y \,dy \,dx\) for \(a=1, 3\).

      >>> f = lambda y, x, a: a*x*y
      >>> integrate.dblquad(f, 0, 1, lambda x: x, lambda x: 2-x, args=(1,))
          (0.33333333333333337, 5.551115123125783e-15)
      >>> integrate.dblquad(f, 0, 1, lambda x: x, lambda x: 2-x, args=(3,))
          (0.9999999999999999, 1.6653345369377348e-14)

  Compute the two-dimensional Gaussian Integral, which is the integral of the Gaussian function \(f(x,y) = e^{-(x^{2} + y^{2})}\), over \((-\infty,+\infty)\). That is, compute the integral \(\iint^{+\infty}_{-\infty} e^{-(x^{2} + y^{2})} \,dy\,dx\).

      >>> f = lambda x, y: np.exp(-(x ** 2 + y ** 2))
      >>> integrate.dblquad(f, -np.inf, np.inf, -np.inf, np.inf)
          (3.141592653589777, 2.5173086737433208e-08)