how to find matrix integral

in my programming i find 6*6 matrix 
i need to find  exponential of matrix (expm(a*t)) , after that got result i try fo find convolution integral ,however matlab can not find it i tried vpa  unfortunately  i didn't get any answer !!  
so how can i find convolution integral of matix or multiply matrix convolution integral ,

Answer 1

[Gang-Gyoo]

You can calculate exp(at) using 'c2dm'. Refer to the following code. aa is what you want with a specific sampling time Ts.

a= [0 1;-1 -2]; Ts= 0.1;
[aa,bb,cc,dd]= c2dm(a,[],[],[],Ts)