Integration of numerical data

I have a set of numerical data stored in a vector D, and a second vector of positions z, of equal length.

If i wish to calculate the integral shown in the picture, how would this be done?

Answer 1

[John D'Errico]

Multiply the two vectors. Then call trapz.

Answer 2

[Star Strider]

For vectors of data, the best option would be the trapz (link) or the related cumtrapz functions, depending on the result you want.

[Abdul Basith Ashraf]

I have not so regular data (x and y are returned from ode45).

How can I visualize the rectangles under the curve to see how good trapz is doing?