MATLAB: How to Use plot::Inequality From Symbolic Math Toolbox

plottingr2011asymbolictoolbox

I have the Symbolic Math Toolbox installed in my copy of Matlab R2011a, and I found http://www.mathworks.com/help/toolbox/mupad/plot/PRIMITIV_Inequality.html#static.

However, the example code here does not work. Matlab complains about the "::" notation, and also the ".." notation being used. Does anyone know why?

Best Answer

That command syntax is appropriate when you are inside a mupad notebook. To call the function from MATLAB, you need to use

evalin(symengine, 'plot(plot::Inequality(x^2 + y^2 < 1,x = -1.5..1.5, y = -1.5..1.5))')

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MATLAB: How to create a symbolic integer in the Symbolic Math Toolbox

If you are using the MuPad symbolic engine from Symbolic Toolbox (R2008b) or higher, you can use the ASSUME function from MuPad as follows:

syms x
evalin(symengine,'assume(x,Type::Integer)')

To remove assumptions from the variable x, you can use the following command:

syms x clear

If you are using Symbolic Toolbox (R2008a) or before, you will also need the Extended Symbolic Toolbox to do this. The Maple function ASSUME allows you to add assumptions to a symbolic variable. The following example demostrates the creation of a symbolic integer variable:

syms x
maple('assume(x,integer)');

MATLAB: Inequality problem

You have to split them up... instead of:

A < X < B

you have to do:

(A < X) && (X < B)

Incidentally, make sure you are using good logic. At your first if you have:

0.00 > X < 0.25

which is the same(*) as saying:

(X < 0.0) && (X < 0.25)

The second part is redundant, because if X is less than 0.0 it is also less than 0.25

(*) By saying "same" I mean the way you would interpret the statement. Matlab executes those two statements very differently.

Best Answer

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MATLAB: Inequality problem

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