MATLAB: I’m really stuck here….

MATLABsymbolicsyms

I need to create a program which will ask the user to input a symbolic expression in x, then display the first and second derivatives and graph the (original) expression in an appropriate window and highlight all roots, critical values, and inflection points.

I know to use syms for this, but I'm stuck on this problem.

Best Answer

doc syms
doc diff
doc ezplot
doc text

Related Solutions

MATLAB: A question about the evaluation of a derivative obtained via “syms” command

P = sym('some expression');
Px = matlabFunction(diff(P,x));

MATLAB: How to get the minima of a parabola

I don’t see why you need to use the Symbolic Math Toolbox for this. I suggest:

% Create data:
tol = linspace(1,10,7);
pix = polyval(poly([1 3 5]),tol) + 0.5.*(rand(1,7)-.5);
% Fit: 
a = polyfit(tol,pix,3);
d1a = polyder(a);               % First derivative
d2a = polyder(d1a);             % Second derivative
ip = roots(d1a);                % Inflection points
mm = polyval(d2a,ip);           % Second derivative evealuated at inflection points
fprintf(1,'\n\tMinimum at %.3f\n', ip(mm>0))
fprintf(1,'\n\tMaximum at %.3f\n', ip(mm<0))
figure(1)
plot(tol, pix, '-b')
hold on
plot(ip, polyval(a,ip), '+r')
hold off
grid

If you get complex roots, this becomes more interesting to plot but the maths are the same.

Best Answer

Related Solutions

MATLAB: A question about the evaluation of a derivative obtained via “syms” command

MATLAB: How to get the minima of a parabola

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