Multiple specific elements in an array

I have a matrix [a b c d e f g]. I want to sum [2*(a + b) + 3*(c+d) +4*(e+f)]. How do i go about doing this ?

Answer 1

[Bhaskar R]

Assuming a, b,c, d, ..g are values in the vector say X

X = 1:7;
sum([2:4].*[sum(reshape(x(1:6), 2,3))]);

[rockstar49]

Hi Bhaskar,

So far my code is:

clc

clear

values=input('Enter P(x)-Using [p1 p2 p3 etc] for uniform/nonuniform dist. \n');

x=[values]; User enters: '[.36 .14 .13 .12 .1 .09 .04 .02]'

y=-(values.*log2(x));

H=sum(y); %sum of all P(x) values to determine expected code length

fprintf('The average code length H(x) is: %d\n', H);

Now i want to sum 2*.36 + 3*(.14 + .13 +.12 +.1 +.09) +4*(.04 +.02)

Thank you for the input!

Zakir

[Bhaskar R]

Your question is different from your comment

"sum [2*(a + b) + 3*(c+d) +4*(e+f)]"

"Now i want to sum 2*.36 + 3*(.14 + .13 +.12 +.1 +.09) +4*(.04 +.02)"

[rockstar49]

Should I post it as another question ?

[Bhaskar R]

No, I mean to say that you have asked for "sum [2*(a + b) + 3*(c+d) +4*(e+f)]" then asking for "Now i want to sum 2*.36 + 3*(.14 + .13 +.12 +.1 +.09) +4*(.04 +.02)". Each time we can't change the evaluation of the statement. If there are only less than 10 entries you can write complete statement without using any commands using matlab indexing.

for this

sum 2*.36 + 3*(.14 + .13 +.12 +.1 +.09) +4*(.04 +.02) =

res = sum([2*x(1), 3*x(2:6), 4*x(7:8)]);

For information on indexing https://in.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html

I think i am clear!

[rockstar49]

thank you! I did not know of this.

Best,

Zakir M