Semilogy with two functions - how to make it work?

I have two functions, y1 and y2, both of which are quadratic functions. I'm trying to graph them on the same plot, with the y-axis being on a logarithmic scale instead of a linear scale. I know how to get just one of the functions to have a log scale on the y axis, but whenever I have two functions involved, the y-axis reverts to a linear scale. I have the code I've been using below; how might I format the semilogy so that the plot will have both functions graphed while still having the y-axis as a logarithmic scale? Any help would be appreciated.

Code:

x1=0:0.1:50;
x2=0:0.1:50;
y1=15*(x1.^2);
y2=80*(x2.^2);

semilogy(y1,y2)
plot(x1,y1,'-','LineWidth',3,'Color','k')
hold on
plot(x2,y2,'-','LineWidth',3,'Color','k')

Answer 1

[the cyclist]

x1=0:0.1:50;
x2=0:0.1:50;
y1=15*(x1.^2);
y2=80*(x2.^2);

figure
hold on
semilogy(x1,y1,'-','LineWidth',3,'Color','k')
semilogy(x2,y2,'-','LineWidth',3,'Color','k')

[Connor Williams]

This is incorrect. If you initiate the figure with figure and hold on commands before the semilogy command, the figure remains with linear axes.

Answer 2

[Chris]

I think that'll work for now, thank you.

[the cyclist]

Just for your future reference, your remark would have been better placed as a "comment" on my answer (rather than as a new "answer"). You might also consider accepting my answer if it was helpful to you, which may be useful for future users looking for something similar.