Plotting a concatenated function (GUI)

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!

Answer 1

[Stephan]

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))