# Interpretation of integration

1. Oct 17, 2012

### pamparana

Hello all,

I am sorry for this really basic question but am having trouble with visualizing something in my head...

I read up on interpretation of integration as area under the curve by splitting it in strips with Δx as the length of the strip and we have the integral in the limit as Δx→0.

However, I am having trouble visualizing why an integral is considered as summing over a variable. For example, the marginalization operation is described as:

P(x) = $\int$P(x, y) dy

I am having even trouble explaining this problem. I am basically having trouble intuitively thinking why this is marginalization. I can picture this in discrete case easily when

P(x) = $\sum P(x, y)$ for all y.

This is basically calculating the probability for all values of x regardless of whatever value y takes. I can see this clearly but having trouble making the same connection with the integral operator.

Thanks,
Luc

2. Oct 17, 2012

### mathman

3. Oct 17, 2012

### pamparana

Thanks for your reply! The problem I am having is that any discussion that I see explains integral as the area under the curve, which is intuitive and I grasp that.