deval and fplot give strange warnings

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Mariano 2019-4-29

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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 !!!