element wise sum in array

Hello,

I have a formula to calculate value, but, the value of elements will come from some elements of array. Like:

s_k=0.6 * t * x^3 * c^-4

t = [20 30 22 32 10 15 12 14 15 20];

x = [45 34 15 30 22 25 17 20 14 25];

c= [10 10 10 10 10 10 10 10 10 10];

p=[1 3 5 7];

I need the value of sum(s_k(p)).

How can I get that?

Thanks in advance.

Answer 1

[Marta Salas]

You have to use a dot in front of the operation: .* .^ to mean element-wise operation in matlab

t = [20 30 22 32 10 15 12 14 15 20];
x = [45 34 15 30 22 25 17 20 14 25];
c= [10 10 10 10 10 10 10 10 10 10];

s_k=0.6 * t .* x.^3 .* c.^-4

p=[1 3 5 7];
sum(s_k(p));

Answer 2

[dpb]

Good spot for function handle...

>> f=@(t,x,c) 0.6.*t.*x.^3./c.^4
f = 
  @(t,x,c)0.6.*t.*x.^3./c.^4
>> f(t(p),x(p),c(p))
ans =
109.3500    4.4550    6.3888    3.5374
>> sum(f(t(p),x(p),c(p)))
ans =
123.7312
>>