Plotting a function of a function with piecewise limits

조회 수: 10 (최근 30일)
Braden Kerr
Braden Kerr 2020년 9월 25일
댓글: Walter Roberson 2020년 9월 26일
Hello,
I am trying to plot a function of a function, f(x(t)) with piecewise limits, however I keep getting an error that "Subscript indices must either be real positive integers or logicals."
Im wondeirng if I need to adjust my limits im using in my piecewise function so they are in terms of t or if I can leave it in the current form and am missing something else.
t =[0:0.1:2*pi];
x = 2*sin(t);
%% Plot 1
f_1 = piecewise(x<-1, 1.5*x+1.5, 0, -1<x<1, 1.5*x(t)-1.5, x>1);
plot (f_1, t);
Thank you
  댓글 수: 1
Walter Roberson
Walter Roberson 2020년 9월 26일
user asked near duplicate at https://www.mathworks.com/matlabcentral/answers/600166-plotting-a-piecewise-returns-error?s_tid=srchtitle which I have Answered.

댓글을 달려면 로그인하십시오.

답변 (1개)

Dana
Dana 2020년 9월 25일
It's the x(t) that shows up in your definition of f_1: t is a vector of real numbers (including non-integers), so x(t) is not a sensible MATLAB expression. Did you want that to just be x rather than x(t)?
  댓글 수: 2
Braden Kerr
Braden Kerr 2020년 9월 26일
I need to plot f(x(t)) so it should be x(t) and not just x. Seems like easiest may be to plot each piecewise part on the same graph with hold on
Dana
Dana 2020년 9월 26일
No, it shouldn't be x(t), because x(t) doesn't make sense as a MATLAB expression, and that's why you're getting the error you're getting.
For a vector y, the syntax y(j) means the j-th element of y if j is a scalar, and if j is a vector then y(j) = [y(j(1)) y(j(2)) ... ], where j(k) is the k-th element of j.
In your case, t is a vector, so x(t) would put you in the second case above. But t(k) is not typically a positive integer in your case, so there's no such thing as the t(k)-th element of x.
In addition, the use of the symbolic function piecewise is probably not the best way to go about this, not to mention you've messed up the order of your input arguments. Ignoring the x(t) issue, I think you wanted
f_1 = piecewise(x<-1, 1.5*x+1.5, -1<x<1, 0, x>1, 1.5*x(t)-1.5);
I suspect the following will do what you actually want:
t =[0:0.1:2*pi];
x = 2*sin(t);
% The following function returns 1.5*z+1.5 if z<-1,
% 1.5*z-1.5 if z>1, and 0 otherwise
f_1 = @(z) (z<-1).*(1.5*z+1.5) + (z>1).*(1.5*z-1.5);
plot (t,f_1(x));

댓글을 달려면 로그인하십시오.

카테고리

Help CenterFile Exchange에서 2-D and 3-D Plots에 대해 자세히 알아보기

제품


릴리스

R2016b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by