# How to Use Matlab for the Gauss-Newton Method

Written by claire jameson
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The Gauss-Newton method is a nonlinear least squares algorithm. The process involves making a series of guesses as to the value of x, then linearising an equation, say r, near the guesses. The result leads to a new guess, which is a linear least squares solution. The algorithm is repeated until convergence occurs. Performing this method by hand can be arduous process; the use of software such as MathWorks Matlab can perform complicated calculations in a much shorter amount of time.

Skill level:
Easy

### Things you need

• Computer that runs Matlab by MathWorks
• Two nonlinear equations
• Region of estimated convergence

## Instructions

1. 1

Rewrite your equations in the form F(X)=0. When typing the equations into Matlab, don't include the "=0" portion, only the expression to the left of the equals sign.

2. 2

In a new .m file, type the lines "function F=myfun(x)" and "F=[(your first equation);(your second equation)];" without quotation marks. Save this function as "myfun.m" within your Matlab path.

3. 3

On the editor screen, type "x0=[min;max];" where min and max are the minimum and maximum x values of your region of estimated convergence. On the next line, type "options=optimset('Display','iter');" to see the output from the iterations. All commands should be entered without double quotation marks, but single quote marks within the body of the command should remain.

4. 4

To run the algorithm, type "[x,fval] = fsolve(@myfun,x0,LargeScale,'off', NonlEqnAlgorithm, 'gn')" without quotation marks and press enter. The command options for LargeScale and NonlEqnAlgorithm specifiy the procedure for Gauss Newton Method. The answer will display on the screen.

#### Tips and warnings

• Add semicolons to the end of lines if you do not want to see the output. Forgetting semicolons and displaying output could clog the editor screen.

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