How can i use polyval on the input polynomial question?

prompt={'Input Equation:','Value of the variable:'};
dgtitle='Evaluate at a Given Value';
evans=inputdlg(prompt,dgtitle);
eq=str2sym(evans{1});
val=str2double(evans{2});
cf=coeffs(eq);
c=fliplr(cf);
k=polyval(str2double(c),val);
display(k)

k =

NaN

My program should ask for equation and the value of the variable. What did i do wrong?

Answer 1

[David Hill]

Why not just enter the polynomial coefficents instead of an equation?

p=input('Polynomial coefficents, (like [1 2 3 4]):');
val=input('Evaluate at this value');
k=polyval(p,val);
display(k)

[gdwn mmbrv]

teacher required to put polynomials. we're supposed to turn polynomials to coefficients then do the polyval.

[David Hill]

Use regexp() function

y='5x^3+2x^2+3x+5';%requires 1 in front of x's
p=str2double(regexp(y,'(?<!\^)\d*','match'));