# How to create a specific vector c that has two variables x and y ?

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CodeElinesa il 28 Feb 2018
Commentato: Roger Stafford il 28 Feb 2018

the problem here is this vector must be found from c = A\b. A and b are created from two variables x and y. (I posted the image of example xi,yi). x and y come from the normal parabola(ax^2 + bx +c) first, then they could be used in the matrix to form A and b. if my question is too confusing, just see the image...sorry, I am not good at explaining a problem :c Is there a way to solve it ? Thank you.

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CodeElinesa il 28 Feb 2018
yh, i know, if the problem just asks me to use the example x,y values to create c vector, that would be simple. The question is, is there a way to represent the A,b matrix so that any x,y variable could be used?
CodeElinesa il 28 Feb 2018
Modificato: CodeElinesa il 28 Feb 2018
at this moment, I create c = parabola(x,y) for further usage Sorry, I forgot to say input vector x and y are only required to be length 3

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### Risposte (1)

Roger Stafford il 28 Feb 2018
Modificato: Stephen23 il 28 Feb 2018
Assume your xi's and yi's are given by a couple of column vectors, x and y of the same length.
n = length(x);
A = [x.^(n-1:-1:0)];
c = A\y;
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CodeElinesa il 28 Feb 2018
I don't think it makes sense, because you can check my image, A must be 3x3 matrix, and b is 3x1, and what about x^2?
Roger Stafford il 28 Feb 2018
If you have an older version of matlab, use
A = bsxfun(@power,x,((n-1):-1:0));
where again I assume x is a column vector.

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