矩阵函数的图形输出

Question

I have a matrix function with a scalar output, and I would like to plot this as a function of one of the elements of the matrix. The exact function isn't important, so I'll use det for my example:

>> fplot(det([x 0;0,1]),[0,1000])
Error using vertcat
CAT arguments dimensions are not consistent.

alternatively:

>> x=linspace(0,1000,1001);
>> plot(det([x,0;0,1]))
Error using vertcat
CAT arguments dimensions are not consistent. 

I'm sure this is simple, and there just a trick which googling hasn't revealed.

Answer 1

x=linspace(0,1000,1001);
plot(det([x,0;0,1]))

This is a problem: [x,0;0,1]

because x has 1001 elements so your top row (ie [x,0] ) is 1002 elements and your bottom row is just 2 elements. And you're trying to vertically concatenate them ie the [;] operator. This only works if both rows have the same number of columns.

I'm not sure exactly what you're trying to plot so I can't recommend a fix, you'll have to explain the problem a bit better first.

Answer 2

This is possible (as I knew it would be) using fplot . But the command has to be fplot('det([x,0;0,1])',[0,1000]) (note the quotes). In fact my ancient (matlab 5) paper manual says:

"The most common mistake in using fplot (as well as other numerical analysis functions) is forgetting to put the name of the function in quotes That is fplot needs to know the name of the function as a character string"