There are a number of ways you can proceed. One way is to use 'int' with a variable upper limit. See:
http://www.mathworks.com/help/symbolic/int.html
If that does not succeed (which often happens) you can do numerical integration using the 'cumtrapz' function which also allows you to have a variable, though discrete, upper limit. See
http://www.mathworks.com/help/matlab/ref/cumtrapz.html
Finally, there are several functions in the File Exchange which are numerical but have higher precision. I wrote one of these. It is located at:
http://www.mathworks.com/matlabcentral/fileexchange/19152-cumulative-cubic-integration
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