


A lot of times it happens that you have a definite integral, depending
on one or more external parameters, and you would like to see how the
value of the integral varies as you vary those parameters. For example,
consider the function
What does this integral look like as a function of the parameter M? There are two approaches to this question. One is actually to sit down and put a little thought into it. This, however, gets to be a hassle, especially on those days when you really just can't be bothered to think. In such cases it is convenient to be able to fall back on the second, noactualbrainpowerrequired solution, which I call The Grinter, which I think is short for "graphical integrator."
% grinter 
I think the GUI is pretty selfexplanatory. You can have up to three
numerical parameters and up to three nested integrals. You can enter
arbitrary numbers, or infinity and infinity ,
in the boxes for lower and upper integration bounds. You can save the
data to a file with a name of your choosing. You can use logarithmic
scales for either or both axes. You can tweak the numerical integration
parameters. Once you have configured your choices, clicking the
Go button will pop up a plot of your output:

Grinter.20080426.tar.gz 
To build the code you will need FLTK (including FLUID) and the GSL. To run it you will also need gnuplot. If anybody is actually reading this and has issues getting the software to build and/or run, let me know. 
Basically, the program just captures the user's input from the GUI window,
writes out a little C program invoking the GSL numerical integration
routines (with the character strings entered in the Integrand:
boxes copied verbatim to be executed as C expressions), compiles and
executes the little C program, and then invokes gnuplot to plot the
results. There is no error checking at any step, so if you click
Go and nothing happens then it could be that (a) the program didn't
compile, maybe because you have a typo in your integrand expression (or
the expression used a symbol that you didn't declare as a parameter or
a variable of integration), or (b) the program compiled but the numerical
integrator failed, maybe because your integral diverged, or (c) some other
reason.

The GRINTER, by Homer Reid 

Last Modified: 11/16/16 