Parse error at ')'when plotting surface plot

Hey, I'm trying to plot the surface plot z=(x^2-ycos(x))/sqrt(x^2+y^2)

Everytime I try to run the program though, it keeps coming up with the error: "parse error at ')': usage might be invalid Matlab syntax" after the cos(x.) in the equation. Any help would be much apreciated :)

x=-5:.1:5;y=x;[x,y]=meshgrid(x,y);
z = (x.^2-y.*cos(x.))/sqrt(x.^2+y.^2);
surfc(z)
xlabel('x axis')
ylabel('y axis')

Answer 1

[Walter Roberson]

In MATLAB, periods in source code must be in one of the following contexts:

1. in a comment
2. in a single-quoted string
3. in a double-quoted string (R2017a and later)
4. proceeded by a numeric digit, such as 35.
5. followed by a numeric digit, such as .35
6. followed immediately by * or ^ or / such as 3.*5 or 3.^5 or 3./5
7. between two variable names, or two parts of a package name, indicating structure access or property access or method invocation, such as MyStruct.field7 or matlab.lang.makevalidname
8. after a variable name but before a ( indicating dynamic field access, such as MyStruct.(fn{3})

In your expression cos(x.) this is not any of the cases.

MATLAB does not permit abbreviating floating point 0 as just plain . requiring instead 0 or 0. or .0 . And if it did accept plain . as 0, it would still be an error to have written cos(x 0) without an operator between the x and the zero.

[Eric Yeh]

Thanks for the help!

My professor said that having the variable as x. allows matlab to treat it as a vector.

However, when I try using it as x.0 or x.^1, it comes up with the error that there are missing ')' or a warning that "the matrix is singular to working precision". When I try to plot the latter scenario, nothing comes up in the figure.

Would you have any ideas on how to write out the equation with proper syntax and be plotted?

[Walter Roberson]

Use ./ instead of /