Plotting Anonymous Function of two variables

Hello,

I have defined the following Anonymous Function of two variables:

f1 = @(x) erf(x(1))+cos(x(2));

When writing the command for plotting via fsurf

fsurf(f1,[-5 0 -5 5])

Error using surf
Z must be a matrix, not a scalar or vector.

I get the following warning and my figure remains empty:

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize

your function to return an output with the same size and shape as the input arguments.

So, what am I doing wrong?

I know that I can plot the function with

f1 = @(x,y) erf(x)+cos(y);
fsurf(f1,[-5 0 -5 5])

but I want to plot it like at the beginning.

How can I plot a Anonymous Function that is defined as mentioned at the beginning?

Regards,

Michael

[Dyuman Joshi]

"I have defined the following Anonymous Function of two variables:"

No, that is an anonymous function of a single variable i.e. x.

From the documentation of fsurf - "Specify a function of the form z = f(x,y). The function must accept two matrix input arguments and return a matrix output argument of the same size."

"How can I plot a Anonymous Function that is defined as mentioned at the beginning?"

Any particular reason why you want to use that approach?

[Michael Haag]

Thank you for the hint to the doc of fsurf.

Yes, there is a particular reason. When doing some optimization with i.e. fmincon, the objective function has to be defined as mentioned and if I want to plot that function I cannot do this easily with fsurf.

What is your recommendation to plot the function defined by

f1 = @(x) erf(x(1))+cos(x(2));

?

[Matt J]

When doing some optimization with i.e. fmincon

For situations like that, I would do,

s = @(x1,x2) erf(x1)+cos(x2); %use this for surface plotting

objective = @(x) s(x(1), x(2)); %use this for fmincon

[Dyuman Joshi]

"the objective function has to be defined as mentioned"

I am bit skeptical about "has to".

Can you give more details about what you are trying to? Can you share the objective function?

[Michael Haag]

s = @(x1,x2) erf(x1)+cos(x2); %use this for surface plotting
objective = @(x) s(x(1), x(2)); %use this for fmincon

This is exactly what I need! Thanks a lot.

@Dyuman Joshi: I just want to minimize a simple function. My intention was to figure out how to define the function thta I am able to minimize it with fmincon and to plot it afterwards.

Answer 1

[Matt J]

f1 = @(x) erf(x(1))+cos(x(2));

fsurf(@(x1,x2) f1([x1,x2]) , [-5 0 -5 5])

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize your function to return an output with the same size and shape as the input arguments.

[Michael Haag]

Thank's a lot. But the warning is still issued. Is there a nicer way to do the plotting with the function defined as mentioned?

[Matt J]

You're welcome, but please Accept-click the answer.

No, you cannot avoid the warning with the input syntax you've chosen, except with warning off.

f1 = @(x) erf(x(1))+cos(x(2));

warning off
fsurf(@(x1,x2) f1([x1,x2]) , [-5 0 -5 5])

warning on