Plotting a concatenated function (GUI)

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Susan G
Susan G 2019-6-20
编辑： Stephan 2019-6-21
I have created a GUI interface that allows a user to enter three different values (a, b, c) which are coefficients for a quadratic equation. I am trying to then plot the quadratic equation on axes1 in the GUI interface.
testa=(get(handles.a,'String'));
testb=(get(handles.b,'String'));
testc=(get(handles.c,'String'));
testfun=strcat(testa,'.*x.^2+',testb,'.*x+',testc);
x=-5:.5:5;
axes(handles.axes1)
plot(x,testfun)
I get the following error:
Error using plot
Error in color/linetype argument.
I know what the error is. Passing testfun as a string to plot doesn't work. I've tested the following through the command line:
x=-5:.5:5
funy1=1.*x.^2+5*x+6
funy2='1.*x.^2+5*x+6'
plot(x,funy1) worked and plot(x,funy2) did not work.
So....my question is if I have to concatenate inputs from the GUI (a,b,c) with the '.*x.^2+' and '.*x+" to get my equation to graph, how can I make it without the single quotes (i.e. not a string) so I can plot the equation that I created through the concatenation process?
Thanks for your time and feedback!

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采纳的回答

Stephan
Stephan 2019-6-21
编辑：Stephan 2019-6-21
https://de.mathworks.com/help/matlab/ref/str2func.html
x=-5:.5:5
funy2=str2func('1.*x.^2+5*x+6')
plot(x,funy2(x))

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