Is there any notation for the calculation of this sum ??

I want to calculate a sum of products of the form :

1.1*a^2*b^9+1.4*a^7*b^4+0.25*a^6*b^8

where a and b are constants.

This expression is the sum of 3 products, I am giving it just for simplification, but the reality is that I have to calculate a sum of 47 products of this form and in each product the coefficients (1.1, 1.4, 0.25) are different and the powers (2, 9, 7, 4, 6, 8) are also different from one product to the other.

So, my question is : Is there any notation that I can use to calculate the sum above without having to repeat each time the constants a and b ??

Answer 1

[Azzi Abdelmalek]

example

x=11
a=[1 2 3 4];  
p=[10 15 20 25]
sum(a.*x.^p)

% the result is

a(1)*x^p(1)+a(2)*x^p(2)+...

./ and .* and .^ are operations element by element

for your case

c=[1.1 1.4 0.25 ]
p1=[2 7 6]
p2=[9 4 8]
a=10;b=30
out=sum(c.*a.^p1.*b.^p2)

you can also create a function

f1=@(c,p1,p2,a,b) sum(c.*a.^p1.*b.^p2)

then

out=f1(c,p1,p2,a,b)

Answer 2

[kamal kiki]

Thank you very much Abdelmalek for your answer.

I am still having a problem.

I have saved the M-file below under the name mytotal.m

    function F = mytotal(c,p1,p2,a,b)

    F = @(c,p1,p2,a,b)sum(c.*a.^p1.*b.^p2)

But when I enter in the command window the following command

mytotal([1.1 1.4 0.25 ],[2 7 6],[9 4 8],10,30) I have the following output

ans = @(c,p1,p2,a,b)sum(c.*a.^p1.*b.^p2) displayed in the command window.

Please what is wrong in my M-file ?????

[Azzi Abdelmalek]

Kamal it's not a function file. just write

f1=@(c,p1,p2,a,b) sum(c.*a.^p1.*b.^p2)

then

c=[1.1 1.4 0.25 ]
p1=[2 7 6]
p2=[9 4 8]
a=10;b=30
out=f1(c,p1,p2,a,b)

[kamal kiki]

Ok thank you very much Abdelmalek.

Answer 3

[Wayne King]

Why are you entering it like that?

 mytotal = @(c,p1,p2,a,b)sum(c.*a.^p1.*b.^p2)
 mytotal([1.1 1.4 0.25 ],[2 7 6],[9 4 8],10,30)