Please help. why is this not graph not working. I'm trying to print the graph of y'' + y' + y = 0 and y'' + y' + y = cos(x)

x = linspace(0,10,100)

y = exp(-x/2)*cos((3^(1/2)*x)/2) + exp(-x/2)*sin((3^(1/2)*x)/2)

y1 = exp(-x/2)*cos((3^(1/2)*x)/2) + exp(-x/2)*sin((3^(1/2)*x)/2) + sin(x)

plot(x, y, 'o', 'MarkerEdgeColor', 'k', ...

'MarkerFaceColor', 'g', ...

'MarkerSize', 4)

hold on

plot(x, y1)

title('exp(-x/2)*cos((3^(1/2)*x)/2) + exp(-x/2)*sin((3^(1/2)*x)/2) + sin(x)')

legend('homogeneous','inhomogeneous')

xlabel('x')

ylabel('y')

Answer 1

[Star Strider]

You need to vectorise your equations.

Also in the plot title, you need to enclose the values in curly brackets ‘{}’ that you want included in special operations, here exponents.

This works:

x = linspace(0,10,100);
y = exp(-x/2).*cos((3^(1/2).*x)/2) + exp(-x/2).*sin((3^(1/2)*x)/2)
y1 = exp(-x/2).*cos((3^(1/2)*x)/2) + exp(-x/2).*sin((3^(1/2)*x)/2) + sin(x)
plot(x, y, 'o', 'MarkerEdgeColor', 'k', 'MarkerFaceColor', 'g', 'MarkerSize', 4)
hold on
plot(x, y1)
title('exp(-x/2)*cos((3^{1/2}*x)/2) + exp(-x/2)*sin((3^{1/2}*x)/2) + sin(x)')
legend('homogeneous','inhomogeneous')
xlabel('x')
ylabel('y')

For more information on vectorising your code, see the documentation for Array vs. Matrix Operations.