Help to transform math formula to matlab

Hello,

I am trying to transform this formula into matlab, but I can't use a for/while loop. X is an array with dimension n and every position receives this sum.

I tried like this, but I couldn't remove the loop here, can I achieve this without a loop?

I also tried to use arrayfun, but without success because every position of the array was receiving the same value.

[Dave B]

Is there are part of the sum that you can pull out?

(is sum(100*j) different from 100*sum(j)?)

[Matthew Lima]

I'm sorry, I really let that pass. So I can remove the log(i) from sum, right?

[Dave B]

That sounds like a good idea to me!

[Matthew Lima]

Thank you!

There is a way of achieving that without a loop?

[Dave B]

There sure is! Break it down, now that you've got the i part out of the sum, where would you think you need a loop?

[Matthew Lima]

Thank you so much Dave, I am new to Matlab i didn't realize how simple it is.

Thank's for the clear explanation.

[Dave B]

Ah I was trying to avoid doing it for you so that you could feel the satisfaction :) Glad it feels simple, hope it stays that way as you delve deeper!

note this is the simplified version of what you wrote:

x = log(1:n) * sum(exp((1:m).^2))

Answer 1

[Sulaymon Eshkabilov]

Using the vectorization:

format long
m=5;
jj=1:m;
XSum1 = sum(log(jj).*exp(jj.^2))

XSum1 = 
     1.158997425794889e+11

% Or alternatively
Xs = log(jj).*exp(jj.^2);
XSum2=sum(Xs)

XSum2 = 
     1.158997425794889e+11

% Sum stepby-step:
cumsum(Xs)

ans = 1×5

1.0e+11 * 0 0.000000000378446 0.000000089399921 0.000123277048990 1.158997425794889

[Dave B]

Note that i and j are not the same in the question, the correct answer here is:

x = log(1:n) * sum(exp((1:m).^2))

as discussed in the comments above.