# Derivative over double summation?

19 views (last 30 days)

Show older comments

##### 4 Comments

David Goodmanson
on 13 Jan 2019

Hi Samuel,

so by dP/dm do you mean a matrix whose ij component is dP/dm_ij?

Also the summand in each of the double sums defining P is identical, so the two double sums are almost identical, differing only in slight chages in the upper limits. Is this what is intended?

### Answers (1)

Walter Roberson
on 13 Jan 2019

The derivative of absolute value is not well defined.

##### 8 Comments

Walter Roberson
on 14 Jan 2019

The solution is as I gave before with the difference of sign() , but remember you need to be careful on the boundary condition .

The derivative is 0 except for at most two terms because the m variable are independent except the two cases of identical subscripts. So you can break it down to three cases, one for each of the two boundary conditions and one for the centre. You can then vectorize for the centre and vectorize for each of the two boundary conditions . or perhaps it works out to be four boundary conditions . Small number of them anyhow .

### See Also

### Categories

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!