representing simple definite integral as convolution in matlab using CONV
A definite integral is a convolution with idial all '1' filter(by the theory)


No. Where does that theory come from ?

If you want to approximate a definite integral with a discrete sequence, you can simply sum up the samples in the integration interval and scale the sum by the sampling interval.

The output of a convolution of two functions is another function, not a single value.