Improper Integral calculation within a tolerance

function r = myimproperintegral(f,a,b,tol)

syms x;

first = int(f,x,a+(b-a)/2,b);

second = int(f,x,a+(b-a)/3,b);

z = 4;

while ((second - first) > tol)

      first = second;

      second = int(f,x,a+(b-a)/z,b);

      z = z+1;

end

r = second;

This is the current function I have written so far in attempt to calculate an improper integral to a certain tolerance, but for some reason when I test it with some values i get an error in the while loop condition that states "Conversion to logical from sym is not possible". Any insight on this would be appreciated as I'm not sure what is going on, thanks.

[Geoff Hayes]

Hugo - put a breakpoint at the line for

 first = int(f,x,a+(b-a)/2,b);

and then run the code. When the debugger pauses at this line, step over it. What is the value for first? Step over the next line. What is the value for second?

See this tutorial for tips on debugging in MATLAB.