topic Re: Mathcad 15 index summation in Mathcad

Mathcad 15 index summation

JB_10220769 — Wed, 29 Jun 2022 20:56:31 GMT

Is it possible to to index the summation for odd numbers in 15?

Re: Mathcad 15 index summation

Werner_E — Wed, 29 Jun 2022 22:03:28 GMT

Maybe that way:

Re: Mathcad 15 index summation

Werner_E — Wed, 29 Jun 2022 22:17:39 GMT

Or you may redefine your function f(..) to return zero for even values of n:

or, as a variation, you may put the branch into the sum instead of the function f:

And as my last solution for now you may do without the summation operator and program the summation yourself:

The last will not work for a=1 unless you add some kind of branch (if).

Re: Mathcad 15 index summation

JB_10220769 — Tue, 05 Jul 2022 13:57:37 GMT

I tried to follow the same method in my original programming but the solution does not converge while matlab can

Can you share your views

Re: Mathcad 15 index summation

Werner_E — Tue, 05 Jul 2022 15:23:57 GMT

You may want to look at the functions An and k_n.

The constant factor in C_b is a quite low pure imaginary number and for most odd values of n the summand is a very small imaginary number , too. But for some odd values of n the summands seem to "explode".

This may also be due to numerical inaccuracies - compare the result of the numeric to the symbolic evaluation shown in the picture for b=21. But both values are quite large so you may want to recheck your function definitions.

There is also a significant difference when I evaluate C_b (for m=41) when evaluated symbolically:

I just noticed that when you define the function An you already have k_n(n,h) in the denominator. When you define C_b you have the same function again in the denominator of the summands. Guess this was not done on purpose?

BTW, you should omit the first argument n in your function definition of C_b as n is the summation index anyway.