Matlab help. Can't figure out why this wont work

[LakeMountD]

for r = 2:.1:10
h=(500/(pi*r^2))-(2*r); %Height for given r assuming max volume of 500m^3
a=2*pi*r*h; %Surface area for cylindrical part
b=2*pi*r^2; %Surface area for hemispherical top
t=a*300+b*400; %Total cost using values of surface area
plot(r,t,'r-+');
end

I am just trying to get it to plot each r value against its respective cost (t value) but it only gives me one point on the graph. Why won't it create a string of points?

 

[Cyrus]

because you lack an index. Just do this:

r = 2:.1:10;
h=(500/(pi*r.^2))-(2.*r); %Height for given r assuming max volume of 500
m^3
a=2*pi*.r*h; %Surface area for cylindrical part
b=2*pi*r.^2; %Surface area for hemispherical top
t=(a.*300)+(b.*400); %Total cost using values of surface area
plot(r,t,'r-+')

 

[LakeMountD]

? Error using ==> /
Matrix dimensions must agree.that is the error I am getting when i tried it the way you just posted.. any ideas?

 

[Cyrus]

r = 2:.1:10;
h=(500./(pi*r.^2))-(2.*r); %Height for given r assuming max volume of 500
m^3
a=2*pi*.r*h; %Surface area for cylindrical part
b=2*pi*r.^2; %Surface area for hemispherical top
t=(a.*300)+(b.*400); %Total cost using values of surface area
plot(r,t,'r-+')

Does that work?

 

[LeBrad]

figure;hold on
for r = 2:.1:10
h=(500/(pi*r^2))-(2*r); %Height for given r assuming max volume of 500m^3
a=2*pi*r*h; %Surface area for cylindrical part
b=2*pi*r^2; %Surface area for hemispherical top
t=a*300+b*400; %Total cost using values of surface area
plot(r,t,'r-+');
end

You can do it one point at a time like you originally had, but you have to add "figure; hold on" before the loop. Now every time you do plot(r,t) it will add points to the plot, rather than replace the previous point.

 

[Cyrus]

Arg, why. Thats such a waste of CPU speed and its really bad coding.

 

[LeBrad]

Arg, why. Thats such a waste of CPU speed and its really bad coding.

clear all
tic
r = 2:.1:10;
h=(500./(pi*r.^2))-(2.*r); %Height for given r assuming max volume of 500 m^3
a=2*pi.*r.*h; %Surface area for cylindrical part
b=2*pi*r.^2; %Surface area for hemispherical top
t=(a.*300)+(b.*400); %Total cost using values of surface area
figure;plot(r,t,'r-+')
toc

clear all
tic
figure;hold on
for r = 2:.1:10
h=(500/(pi*r^2))-(2*r); %Height for given r assuming max volume of 500m^3
a=2*pi*r*h; %Surface area for cylindrical part
b=2*pi*r^2; %Surface area for hemispherical top
t=a*300+b*400; %Total cost using values of surface area
plot(r,t,'r-+');
end
toc

Elapsed time is 0.123388 seconds.
Elapsed time is 0.125952 seconds.
>>

Oh no, 0.0026 seconds! All my CPU speed are belong to Matlab.