Attempting to plot a function with a for loop, but nothing is working.

This is my first time posting a question...I'm getting stuck on this portion of my code.

1: I can't seem to figure out why my function won't plot at all.

2: I can't figure out how to plot multiple lines on one plot.

figure(1);
for i = 1:2:50										%for loop to run for 2miles of radius, or 1 hr of time
	con = (kilotons * (1.2*10^8))/(pi*i^2);			%Formula for calculating the concentration at each interval
	plot(i,con)										%plots hours/radius against concentration
	ylabel('Concentration'), xlabel('Time (hr)')	%Labels plot
	title('Decreasing Concentration By Hour')
	grid on
	hold on											%Supposed to hold each plot as the for loop moves through its sequence
end
hold off

[Wyatt Leuck]

For the future: I ended up using this...

figure(1);
for ii = 1:10
xdata = 1:2:50;
ydata= (kk*1.2*10^8)./(pi*xdata);
plot(xdata,ydata)
ylabel('Concentration'), xlabel('Time (hr)')	
title('Decreasing Concentration By Hour')
grid on
hold on
end

[Michael Van de Graaff]

Presumably you meant

ydata= (ii*1.2*10^8)./(pi*xdata);

since kk hasn't been defined?

but yeah, that plots pretty lines. you can modify as follows:

figure(1);
for ii = 1:10
xdata = 1:2:50;
ydata= (ii*1.2*10^8)./(pi*xdata);
plot(xdata,ydata,'displayname',['ii = ',num2str(ii)]) % this will tell a legend object what to label, handy
ylabel('Concentration'), xlabel('Time (hr)')	
title('Decreasing Concentration By Hour')
grid on
hold on
end
legend % without calling legend it won't show up.

Do keep in mind that legend is much slower than everything else in matlab.

Answer 1

[Michael Van de Graaff]

figure(1);
kilotons = 2; %i needed to add this
% i always use double indices ii,jj,kk, helps avoid confusing and also is
% i=sqrt(-1)?
for ii = 1:2:50										%for loop to run for 2miles of radius, or 1 hr of time
	con(ii) = (kilotons * (1.2*10^8))/(pi*ii^2);			%Formula for calculating the concentration at each interval
	plot(ii,con(ii),'o')	% the plotmarker 'o' is key if you INSIST on doing it this way									%plots hours/radius against concentration
	ylabel('Concentration'), xlabel('Time (hr)')	%Labels plot
	title('Decreasing Concentration By Hour')
	grid on
	hold on											%Supposed to hold each plot as the for loop moves through its sequence
end
hold off

The important part is using plot works best with vectors, and it defaults to line plots, so your data ARE there, but the plot markers aren't visible.

I would do it this way:

figure(1);
kilotons = 2;
xdata = 1:2:50;
ydata= (kilotons*1.2*10^8)./(pi*xdata)
plot(xdata,ydata)
ylabel('Concentration'), xlabel('Time (hr)')	%Labels plot
title('Decreasing Concentration By Hour')
grid on

[Wyatt Leuck]

Hey thanks so much! I really appreciated the comments and pointers you added in. Much help clearing the path!

Answer 2

[David Hill]

kilotons=input('kilotons of blast');
i=1:2:50;
con = (kilotons * (1.2*10^8))./(pi*i.^2);
plot(i,con);
ylabel('Concentration'), xlabel('Time (hr)');
title('Decreasing Concentration By Hour');
grid on;

[Wyatt Leuck]

Awesome! Thanks for the assist!