MATLAB: How to use max inside Simulink Fcn block

functionsimulink

In my Simulink sheet, I have a Fcn block which does a very simple calculation from its input:

u(36)/u(38)*u(39)

Since the input can sometimes assume (unphysical) negative values, I wanted to exlude them:

max(0, u(36)/u(38)*u(39))

But as soon as I call the simulation, I get

The expression: max(0, u(36)/u(38)*u(39))
in '.../.../...'
has a syntax error

So does that mean that max is undefined inside Fcn blocks? If so, what could I use instead?

Math Function Blocks https://www.mathworks.com/help/simulink/slref/mathfunction.html do not accept expressions: they only accept keywords.

You can build max() against a constant with https://www.mathworks.com/help/simulink/slref/minmax.html or with Saturate blocks.

The documentation page shows that you should use sgn instead of sign: https://www.mathworks.com/help/simulink/ref_obsolete_blocks/fcn.html

sgn(u(2)-u(3))

Also, this block is obsolete; consider using a better alternative: https://www.mathworks.com/help/simulink/slref/matlabfunction.html

hi, it does exist, its called "abs" , open Simulink library and go to :"Math operations" block , its the first on the list, with notation u : ABS