How can I plot this equation? keep getting ??? Error using ==> mtimes Inner matrix dimensions must agree.'

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P
P 2013-10-15
评论： P 2013-10-17
The code I have is:
T=[0:0.1:24];
omega=((12-T)/24)*360;
phi=[-180:1:180]
alpha = [0:1:90];
latitude=45;
delta=[-23.5:0.5:23.5];
sind(alpha)=sind(delta).*sind(latitude)+cosd(delta).*cosd(latitude).*cos(omega)
cosd(phi)=(sind(alpha).*sind(latitude)-cosd(delta))./(cosd(alpha).*cosd(latitude))
alpha represents my y-axis and is an angle between 0 and 90 degrees. phi represents my x-axis and is an angle between say -120 to +120.
Whenever I try to input that last line I get the error stating inner matrix dimensions must agree. So I tried to reshape my matrices for those variables I defined so that they work. But then I get '??? ??? Subscript indices must either be real positive integers or logicals.'
It seems very tedious to have to reshape my matrix every time I define a new set of variables in order to use them with an equation. Those variables are used for defining my axis range, is there a better way I can lay them out or an automatic command that will make sure they work every time?
I want to plot alpha and phi as a graph using something like
plot(alpha,phi)
but can't get past those errors? can't I just use a command that says something like define x-axis [0:90], define y-axis [-120:120] or something?
Thanks

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采纳的回答

David Sanchez
David Sanchez 2013-10-16
Define your variables with linspace:
T=linspace(0,24,100);
omega=((12-T)/24)*360;
phi=linspace(-180,180,100);
alpha = linspace(0,90,100);
latitude=45;
delta=linspace(-23.5,23.5,100);
You'll get the same number of elements on each array. Your:
sind(alpha)=sind(delta).*sind(latitude)+cosd(delta).*cosd(latitude).*cos(omega);
cosd(phi)=(sind(alpha).*sind(latitude)-cosd(delta))./(cosd(alpha).*cosd(latitude));
are incongruently defined. What do you really want, alpha or sind(alpha)? why do you define alpha and phi as you did in
phi=linspace(-180,180,100);
alpha = linspace(0,90,100);
?
Do you want something like this?
alpha=sind(delta).*sind(latitude)+cosd(delta).*cosd(latitude).*cos(omega);
phi=(sind(alpha).*sind(latitude)-cosd(delta))./(cosd(alpha).*cosd(latitude));
plot(alpha,phi,'.')

更多回答（1 个）

Image Analyst
Image Analyst 2013-10-16
omega is 1 by 241 while latitude is 1 by 95 so they're not the same number of elements so you can't do an element-by-element sum or product.
  2 个评论
P
P 2013-10-16
Yes I understand that my matrices need to be the same and I can see my error. I guess my question is then: is there a way I can generate my matrices to be the same dimensions from the start so that I don't have this problem but so that they are still for the applicable range of value I need for each variable? I.e 0-90 degrees for an angle and 0-24 hours for time? Any hell is greatly appreciated.
Image Analyst
Image Analyst 2013-10-16
You can use linspace(startingValue, endingValue, numberOfElements) instead of startingValue : stepValue : endingValue to get exactly the number of elements you want.

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