R is the radial coordinate.
B. A C must be less than B and A must be non-negative. A and B are in C radians. This insures that B in the user's program is equal to PI in this C program which permits several tests of the input parameters that C otherwise would not be possible. D. C C must be less than D. C must be non-negative. A two-dimensional array that specifies the values of the right C side of the modified Helmholtz equation.