Why do I receive a "Singularity likely" warning when I use the QUAD function in MATLAB for a function that does not have a singularity?

For example when I execute the following command:

quad(@exp,0,30)

I receive the following warning message:

 Warning: Maximum function count exceeded; singularity likely.

and I receive the following answer:

 ans =

   9.2156e+012

However, I am expecting the answer to be:

 ans =

   1.0686e+013

Answer 1

[MathWorks Support Team]

This warning will occur when the default absolute error tolerance of 1.0e-6 is too small to evaluate the integral in fewer function evaluations than the default 10000.

To work around this issue, specify a larger absolute tolerance as the fourth input argument to the QUAD function. For example, the following command specifies an absolute tolerance of 1:

quad(@exp,0,30,1)

and returns the expected result:

 ans =

   1.0686e+013