Creating a diagram from polynomial

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Berkay
Berkay el 30 de Ag. de 2022
Respondida: Sulaymon Eshkabilov el 30 de Ag. de 2022
I defined a polynomial
P = [1 -2 4]
and I want to draw the shape of polynomial for the range between -10 to 10 with in the logarithmic diagram (only X axis). How can I do it?

Respuesta aceptada

Walter Roberson
Walter Roberson el 30 de Ag. de 2022
Editada: Walter Roberson el 30 de Ag. de 2022
P = [1 -2 4];
x = linspace(-10, 10, 500);
y = polyval(P, x);
lx = log10(x);
rlx = real(lx);
ilx = imag(lx);
plot3(rlx, ilx, y)
xlabel('real(log(x))'); ylabel('imag(log(x))'); zlabel('polynomial value')
You need to use a 3D plot for this because you want a log axes on a range that includes negative values, so you need some way to represent the component of the log of the negative numbers.

Más respuestas (1)

Sulaymon Eshkabilov
Sulaymon Eshkabilov el 30 de Ag. de 2022
There are a few different ways to get this exercise done.
Compute the values of the polynomial P = [1 -2 4] at x = -10:dx:10 with some increment step size (dx) and then plot x vs. y using semilogx(). The code starts with these:
P = [1 -2 4];
dx = ...
x= -10:dx:10;
y = P(1)*x.^2+P(2)*x+P(3);
figure()
...
If you have a difficulty to undertand how to plot the computed values, use help.
>> help semilogx
Moreover, your plotted data will contain the positive values of x and the negative side will be ignored due to a log scale.

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