# I need to perform element by element subtractions within a matrix.

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Sean Flanagan 2022 年 9 月 27 日

I have a 21x2 matrix for a given row say row 12, I need to calculate the errors by using the following numerical schemes; backwards - ((y(12)-y(11)/x(12)-x(11)), forwards - (y(13)-y(12))/(x(13)-x(12), and central (y(13)-y(11))/(x(12)-x(11)). My program needs to use matrix based calculations to solve for each element of the matrix. The following code works for the forward but I cant get the backwards or central working.
yn1 =y(2:length(y));
yn = y(1:length(y)-1);
xn1 =x(2:length(x));
xn = x(1:length(x)-1);
Thanks for the help
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Sean Flanagan 2022 年 9 月 28 日
This is the series of equations I need to satisfy. The matlab script that I have posted solves the forward equation. But I am stuck on the backwards and central equation.

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### 回答 (1 件)

Image Analyst 2022 年 9 月 27 日

Not sure what you mean by the 11, 12, and 13, but why not use the built in diff, conv, and, if you have to flip?
Give an short actual numerical example (inputs and outputs) if you still need help.
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Sean Flanagan 2022 年 9 月 28 日
Thanks for the help mate. Its really apreciated.

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