showing error " Array indices must be positive or logical values"

clc
clear all
N=2;
c=linspace(0.035,0.010,21)
r=linspace(0.0001,1,21)
thetaroot=15;
thetatip=4;
a=5.7
R=0.35;
theta=(thetaroot+(r.*(thetatip-thetaroot)))./57.3
sigma=(N.*c(i))./(pi.*R)
lambda=sigma.*a((sqrt(1+32.*theta.*r)./(sigma(i).*a))-1)

[VBBV]

i & j are complex quantities in Matlab, if you use it as index without assigning any value to them would give such error, since Matlab uses 1 based positive integer indexing

clc
clear all
N=2;
c=linspace(0.035,0.010,21);
r=linspace(0.0001,1,21);
thetaroot=15;
thetatip=4;
a=5.7;
R=0.35;
theta=(thetaroot+(r.*(thetatip-thetaroot)))./57.3;
sigma=(N.*c)./(pi.*R)  % i & j are complex quantities in Matlab

sigma = 1x21

0.0637 0.0614 0.0591 0.0568 0.0546 0.0523 0.0500 0.0477 0.0455 0.0432 0.0409 0.0387 0.0364 0.0341 0.0318 0.0296 0.0273 0.0250 0.0227 0.0205 0.0182

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lambda=sigma.*a((sqrt(1+32.*theta.*r)./(sigma.*a))-1) % same in this line 

Array indices must be positive integers or logical values.

Answer 1

[Torsten]

lambda=sigma.*a.*((sqrt(1+32.*theta.*r)./(sigma(i).*a))-1)

instead of

lambda=sigma.*a((sqrt(1+32.*theta.*r)./(sigma(i).*a))-1)

And since "i" is undefined, c(i) and thus sigma(i) are empty.

[Prasannakumar reddy]

thanks it's working.

[Image Analyst]

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Answer 2

[Image Analyst]

See the FAQ for a thorough discussion of the error:

Subscript indices must either be real positive integers or logicals