deval and fplot give strange warnings

1 view (last 30 days)
Mariano
Mariano on 29 Apr 2019
Hello,
I have found the following strange behaviour:
1) First, I solve an initial value problem for an ode numericall (say, with ode45)
2) Next, I use deval to define a function handle with the solution
3) Finally, I use fplot to plot the function handle.
And here comes the strange thing: for scalar equations, I get a warning from fplot. I have checked this with R2019a and R2018a. I do not have any other release now to test, but I am quite sure I did not get the warning with R2016b.
And what is more strange: for systems of odes, the warning does not appear.
Sample code follows,
Thanks,
Mariano
%% Scalar test
sol = ode45(@(t,y) t*y,[0,1],1);
y = @(t) deval(sol,t);
figure(1),clf(1)
subplot(2,1,1)
fplot(y,[0,1])
% Warning appears:
% Function behaves unexpectedly on array inputs.
% To improve performance, properly vectorize your function
% to return an output with the same size and shape as the
% input arguments.
%
% But the function seems to work properly with array inputs
y([0.27,1/pi])
%% System test
% And more surprinsingly, for systems it works without warnings
sol2 = ode45(@(t,y) [y(2);-y(1)],[0,10],[1;-2]);
y1 = @(t) deval(sol2,t,1);
y2 = @(t) deval(sol2,t,2);
subplot(2,1,2)
fplot(y1,[0,10])
hold on
fplot(y2,[0,10])
% No warning at all !!!

Answers (0)

Products


Release

R2019a

Community Treasure Hunt

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

Start Hunting!