Trouble using ezplot and matlabFunction on a symbolic function defined using symengine "piecewise"

 syms x t;
 MP_syntax1 = 'piecewise([x <= 10, x/10], [10 < x <= 30, (30 - x)/20])';
 MP_syntax2 = 'ilaplace(2/s^3,s,t)';
 f(x) = evalin(symengine,MP_syntax1);
 g(t) = evalin(symengine,MP_syntax2);

No trouble with g(t) or other MuPad functions:

 ezplot(g(t), [-5,5]);
 G = matlabFunction(g(t));

Trying the same to the piecewise, f(x) will not work however.

 ezplot(f(x),[0,30]);
 F = matlabFunction(f(x));

However, this works

 xd = 0:0.1:30;
 fd = double(f(xd));
 plot(xd,fd);

What is wrong with the other calls using ezplot and matlabFunction for f(x) ?

[Geoff Hayes]

Ronny - what do you mean by f(x) will not work? Are you observing an error or something else?

[Ronny Landsverk]

Sorry for beeing unclear. Calling

"ezplot(f(x),[0,30])"  and  "matlabFunction(f(x))"

produces errors. However,

 "ezplot(g(t),[-5,5])"  and  "matlabFunction(g(t))"

produces good output.

Errors are:

 Error using ezplot (line 162)
 piecewise([x <= 10, x/10], [x in Dom::Interval(10, [30]), 3/2 - x/20]) cannot be   plotted in the xy-plane.

and

 Error using symengine>makeFhandle (line 109)
 Error: Unbalanced or unexpected parenthesis or bracket.

 Error in symengine (line 60)

 Error in sym/matlabFunction (line 125)
    g = symengine('makeFhandle',varnames,body);

[Vishal Tripathi]

I am having a similar error. Any solution yet?

[Sarah Palfreyman]

Try the new fplot family of functions in R2016a.

Answer 1

[Sally Al Khamees]

If you have R2016b and the Symbolic Math Toolbox installed, you can just use the piecewise function:

https://www.mathworks.com/help/symbolic/piecewise.html

For example: