I want to use Matlab to draw a quadratic curve of 3 d figure of the original equation is as follows: x ^ 2 + y ^ 2 - (z - 1) ^ 2=0;
Then according to the official document in the matlab as well when there is a error:

I think should be the inside of the square root of number may be negative, and then prescribing becomes a plural, but I don't know how to solve it,,,