how can i make this loop?

hi friends im new in matlab could you please help me in this problem.

I have an equations A ; A=x*a-b

x=[1 2 5 8 10];

i want to put x values into equation A one by one to solve it, which i mean x1=1, to solve A1 and x2=2 to solve A2 and so on.

after that i want to use the results that i found in this equation B= (A1...An / c).

thanks

Answer 1

[Star Strider]

No loop needed.

If you want to calculate ‘A’ with ‘a’ and ‘b’ already defined numerically as scalars, or if ‘b’ is a vector the same size as ‘x’, just do this:

A = x*a-b

If ‘a’ is a vector with the same dimensions as ‘x’, use element-wise multiplication:

A = x.*a+b

You might need to use bsxfun to do the vector multiplications if you have R2016a or earlier.

[Mamad Mamadi]

thanks for your answer Star Strider but i have to say that, if the equation is like this;

A(1,i)=x*a(i,1)

if i=1:20

x=[1 2 5 8 10]

i have to put x=1 to get 20 A, then put x=2 to get another 20 A and x=5 to get another 20 A and so on.

after that i have to put my A results in this equation B= (A1...An / c)

[Star Strider]

I have no idea what ‘a’ is.

Is it a vector or a matrix?

[Mamad Mamadi]

its a 20x1 matrix

[Star Strider]

Then ‘A’ is a (20x5) matrix:

a = rand(20,1);
x=[1 2 5 8 10];
b = rand;

A = a*x - b;

If you have a MATLAB version (release) earlier than R2016b, calculate ‘A’ as:

A = bsxfun(@times, x, a) -b;

to get the same result.

[Mamad Mamadi]

sad to say i use the old version R2013a :(

[Star Strider]

The bsxfun function was introduced in R2007a, so you can use it to do the multiplications. I believe the additions always used explicit expansion. If they do not, use bsxfun for those as well:

A = bsxfun(@minus, bsxfun(@times, x, a), b)

That should work.

The loops are all still there, however they are hidden in the bsxfun calls.