Asked by Nathan Edge
on 11 Oct 2011

Hello, i've written the following script in MATLAB:

Rcon=(Rmax^2) -(Rmin^2);

Ccon= cosd(Thetamin) - cosd(Thetamax);

Scon=sin(Thetamax)-sin(Thetamin);

vN = linspace(0, 180, N); vP = linspace(Thetamin, Thetamax, P);

for iN = 1:length(vN) Phi = vN(iN); G(iN)=Phi + BOC; C2(iN)=Rcon / ((Ccon * cosd(G(iN))) + (Scon * sind(G(iN)))); C1(iN)=Rmax^2 + (C2(iN) * cosd(G(iN) + Thetamax)); A(iN)= (sqrt(C1(iN)+C2(iN)) + sqrt(C1(iN)-C2(iN)))./2; B(iN)=C2(iN) / (2*A(iN));

for iP = 1:length(vP) Theta = vP(iP); R(iP)= sqrt(abs(C1(iN) - (C2(iN) * cosd(G(iN) + Theta))));

F(iN,iP)= abs(((R(iP)*(M*g*L)) *cosd(Theta)) / ... ((A(iN)*B(iN)) * sind(G(iN)+Theta))); Ffinal =max(F);

FFfinal=min(Ffinal);

end end

this script is designed to extract certain values for F as the values for phi and Theta change, where Phi runs from 0 to 180 for a certain number of inputted values (N), and theta lies within P input values, Thetamin and Thetamax. The variable R is also subject to changes in Phi and theta: however, in reality, we know that R falls within a certain range of values (between a maximum, Rmax, and a minimum, Rmin). I have found that with some values of Phi and Theta, the calculated values for R (line 20, including spaces) fall outside of this known range. I'd like to run the script so that I will only calculate F if the calculated value for R falls within the known range. I have attempted to use this command at line 21, but without success:

if Rmin<R(iP) && R(iP)<Rmax

Does anybody have any advice?

Cheers,

-Nathan

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Answer by Andrei Bobrov
on 11 Oct 2011

Accepted answer

for iP = 1:length(vP) Theta = vP(iP); R(iP)= sqrt(abs(C1(iN) - (C2(iN) * cosd(G(iN) + Theta)))); if R(iP) >= Rmin && R(iP) <= Rmax F(iN,iP)= abs(((R(iP)*(M*g*L)) *cosd(Theta)) / ... ((A(iN)*B(iN)) * sind(G(iN)+Theta))); else F(iN,iP) = nan; end Ffinal =max(F); FFfinal=min(Ffinal); end

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## 1 Comment

## Jan (view profile)

Direct link to this comment:http://www.mathworks.com/matlabcentral/answers/17976-selecting-specific-values-in-a-for-loop-when-a-certain-condition-hold-true#comment_39808

Maybe an obvious question: What are the values of Rmin and Rmax? Is Rmin actually smaller then Rmax?

Also, how do you know it is without success? What is the result of your change?