Multiple specific elements in an array

2020 2 20
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更新时间：2020 2 20
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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 ?

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回答（1 个）

Bhaskar R
Bhaskar R 2020-2-20

1 个投票

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))]);

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rockstar49
rockstar49 2020-2-20
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
Bhaskar R 2020-2-20
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
rockstar49 2020-2-20
Should I post it as another question ?
Bhaskar R
Bhaskar R 2020-2-20
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
rockstar49 2020-2-20
thank you! I did not know of this.
Best,
Zakir M

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