# fplot differentiated symbolic equation

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robert hyde le 8 Nov 2017
Hello there!
I'm trying to use the fplot function to plot an equation that I defined previously. However I think because I used syms and the diff() function to create the variable I am trying to plot, it is messing up the fplot function. My output is one graph which I already got to plot and an orange error message saying: '''The following error was reported evaluating the function in FunctionLine update: sym output type is not supported. Set 'UniformOutput' to false.'''
Any ideas for how to solve this? All other threads talk about arrayfun or something unrelated, if not, no worries, but thanks!
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robert hyde le 8 Nov 2017
Modifié(e) : robert hyde le 8 Nov 2017
Here is my code (the error is in plotting Vg):

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### Réponse acceptée

Star Strider le 8 Nov 2017
I would calculate the derivative and create the anonymous function for ‘Vg’ with:
Vg = matlabFunction(diff(Mg,t), 'Vars',{t});
With that change, it runs without error, although the plot generates a long ‘Warning’ message.
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robert hyde le 8 Nov 2017
this worked perfectly and fast, thanks! MVP isn't just a label
Star Strider le 8 Nov 2017
As always, my pleasure!
Thank you very much for your compliment!

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### Plus de réponses (2)

Karan Gill le 8 Nov 2017
You made a simple mistake. You used anonymous functions instead of symbolic functions. Declare a symbolic function using
syms Va(t)
Va(t) = t^2;
and plot it with fplot
fplot(Va)
See the second example in fplot doc: https://www.mathworks.com/help/symbolic/fplot.html
Comment if you have issues. If it works, please accept this answer.
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robert hyde le 8 Nov 2017
This also worked and is a lot simpler to read, so I will use this as I am marked on how my code looks rather than it's run time, thank you very much!

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Omer Ali le 12 Nov 2017
Thanks for asking this Rob! :)
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