Plotting Fourier transform with heaviside functions

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Mario
Mario 2014-7-17
回答： Star Strider 2014-7-17
Hi, when running this code
syms s(t)
syms j(w)
s(t) = 2 * cos(2*t + 1) * heaviside(t - 2*fix(t/2)) * heaviside(-t + 2/10 + 2*fix(t/2));
j(w) = fourier(s, t, w);
ezplot(j);
I get the following output
Error using inlineeval (line 15) Error in inline expression ==> 2.*fourier(heaviside(2.*fix(t./2) - t + 1./5).*cos(2.*t + 1).*heaviside(t - 2.*fix(t./2)), t, w) Undefined function 'fourier' for input arguments of type 'double'.
Error in inline/feval (line 34) INLINE_OUT_ = inlineeval(INLINE_INPUTS_, INLINE_OBJ_.inputExpr, INLINE_OBJ_.expr);
Error in ezplotfeval (line 54) z = feval(f,x(1),y(1));
Error in ezplot>ezimplicit (line 258) u = ezplotfeval(f, X, Y);
Error in ezplot (line 154) hp = ezimplicit(cax, f{1}, vars, labels, args{:});
Error in sym/ezplot (line 61) h = ezplot(fhandle(f));
Error in Untitled5 (line 7) ezplot(j);
Could anyone help me?

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回答（1 个）

Star Strider
Star Strider 2014-7-17
Using the fix function is well-intended but not necessary in symbolic operations. To use heaviside, you need to cast the arguments as symbolic to get a symbolic result. (You can always use matlabFunction to create an anonymous function out of it to use outside of the Symbolic Math Toolbox.)
This works:
syms s(t)
syms j(w)
s(t) = 2 * cos(2*t + 1) * heaviside(sym(t - 2*(t/2))) * heaviside(sym(-t + 2/10 + 2*(t/2)));
j(w) = fourier(s, t, w);
ezplot(j);
although the plot is not informative.

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