fplot Warning: Function behaves unexpectedly on array inputs.

Hello! This SHOULD be a simple fix, and I've spent some time reading answers to similar question.... but still can't manage to find a fix. I'm trying to use fplot to plot lift as a function of length L.

% Lift load
syms q_l ka L x
q_l = ka.*sqrt(L.^2 - x.^2) % Expression for load distribution function

% Integrate expression over the length of wing to calc total load acting on
% wing due to lift
lift = int(q_l,0,L)
lift = subs(lift,ka,150)

% Plot lift as a function of wing length

fplot(@(L) lift,[10 20])

I get the following warnings (no curve is plotted):

Warning: 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.

Warning: Error updating FunctionLine.

The following error was reported evaluating the function in FunctionLine update: Unable to convert expression into double array.

Answer 1

[Star Strider]

The ‘lift’ funciton is symbolic, so no function handle is necessary to plot it with fplot. (If you want to create a funciton handle from it, use the matlabFunction function.)

% Lift load
syms q_l ka L x
q_l = ka.*sqrt(L.^2 - x.^2) % Expression for load distribution function

q_l = 

% Integrate expression over the length of wing to calc total load acting on
% wing due to lift
lift = int(q_l,0,L)

lift = 

lift = subs(lift,ka,150)

lift = 

% Plot lift as a function of wing length

fplot(lift,[10 20])

.

[Emmanuel J Rodriguez]

Thanks @Star Strider

[Star Strider]

As always, my pleasure!

.