expint {VGAM} | R Documentation |
Computes the exponential integral Ei(x) for real values, as well as exp(-x) * Ei(x) and E_1(x).
expint(x) expexpint(x) expint.E1(x)
x |
Numeric. Ideally a vector of positive reals. |
The exponential integral Ei(x) function is the integral of exp(t) / t from 0 to x, for positive real x. The function E_1(x) is the integral of exp(-t) / t from x to infinity, for positive real x.
Function expint(x)
returns Ei(x),
function expexpint(x)
returns exp(-x) * Ei(x),
function expint.E1(x)
returns E_1(x).
This function has not been tested thoroughly.
T. W. Yee has simply written a small wrapper function to call the above FORTRAN code.
http://www.netlib.org/specfun/ei.
## Not run: par(mfrow = c(2, 2)) curve(expint, 0.01, 2, xlim = c(0, 2), ylim = c(-3, 5), las = 1, col = "orange") abline(v = (-3):5, h = (-4):5, lwd = 2, lty = "dotted", col = "gray") abline(h = 0, v = 0, lty = "dashed", col = "blue") curve(expexpint, 0.01, 2, xlim = c(0, 2), ylim = c(-3, 2), las = 1, col = "orange") abline(v = (-3):2, h = (-4):5, lwd = 2, lty = "dotted", col = "gray") abline(h = 0, v = 0, lty = "dashed", col = "blue") curve(expint.E1, 0.01, 2, xlim = c(0, 2), ylim = c(0, 5), las = 1, col = "orange") abline(v = (-3):2, h = (-4):5, lwd = 2, lty = "dotted", col = "gray") abline(h = 0, v = 0, lty = "dashed", col = "blue") ## End(Not run)