Log equation log(x) not plotting correctly

Here is my code. The log(x) function is plotting with negative values.

x=-10:1:10;

y_1=x;

y_2=exp(x);

y_3=log(x);

plot(x,y_1,'k-',x,y_2,'r--',x,y_3,'b:')

hold on

plot([-10 10],[0 0],'k',[0 0],[-5 5],'k')

axis([-10 10 -5 5])

grid on

title('Comparison Between the Exponential and Natural Logarithm Functions')

xlabel('x-axis')

ylabel('y-label')

legend('y=x','y=exp(x)','y=ln(x)')

Answer 1

[Ryan Takatsuka]

y_3 contains complex numbers with real and imaginary components, and the plot() function only plots the real component of the complex number. Imaginary components are ignored.

Answer 2

[Steven Lord]

Did you notice the warning you received in the Command Window when you ran this code?

Does real(y_3) look familiar in the context of your plot?

[Taylor Latham]

This is the warning I received.

Warning: Imaginary parts of complex X and/or Y arguments ignored >>

Answer 3

[James Tursa]

Since you are trying to graph the inverse of the functions, you should be switching the domains as well when you generate the points. So these lines:

y_3=log(x);
plot(x,y_1,'k-',x,y_2,'r--',x,y_3,'b:')

should be this instead:

y_3=log(y_2);  % switched domain of log to y_2 instead of x
plot(x,y_1,'k-',x,y_2,'r--',y_2,y_3,'b:') % same change here