# Why is this variable "undefined"?

4 views (last 30 days)
Alex on 21 Feb 2012
Hey all, here's my code:
%This forgram will take 4 solutions of n1 and solve them.
y = 250;
n0 = 1;
n2 = 1.69;
k2 = 3.67;
R = .75;
for n1 = [2:.01:1.5];
n_new_1 = (pi*d1*n1)/atan((n1*(- R^4*k2^4*n0^2 - 2*R^4*k2^2*n0^3*n2 - 2*R^4*k2^2*n0^2*n1^2 - 2*R^4*k2^2*n0^2*n2^2 - 2*R^4*k2^2*n0*n1^2*n2 - R^4*n0^4*n2^2 - 2*R^4*n0^3*n1^2*n2 - 2*R^4*n0^3*n2^3 - R^4*n0^2*n1^4 - 4*R^4*n0^2*n1^2*n2^2 - R^4*n0^2*n2^4 - 2*R^4*n0*n1^4*n2 - 2*R^4*n0*n1^2*n2^3 - R^4*n1^4*n2^2 + 2*R^2*k2^4*n0^2 + 4*R^2*k2^2*n0^2*n1^2 + 4*R^2*k2^2*n0^2*n2^2 + 2*R^2*n0^4*n2^2 + 2*R^2*n0^2*n1^4 - 8*R^2*n0^2*n1^2*n2^2 + 2*R^2*n0^2*n2^4 + 2*R^2*n1^4*n2^2 - k2^4*n0^2 + 2*k2^2*n0^3*n2 - 2*k2^2*n0^2*n1^2 - 2*k2^2*n0^2*n2^2 + 2*k2^2*n0*n1^2*n2 - n0^4*n2^2 + 2*n0^3*n1^2*n2 + 2*n0^3*n2^3 - n0^2*n1^4 - 4*n0^2*n1^2*n2^2 - n0^2*n2^4 + 2*n0*n1^4*n2 + 2*n0*n1^2*n2^3 - n1^4*n2^2)^(1/2) - k2*n1^3 + k2*n0^2*n1 + R^2*k2*n1^3 - R^2*k2*n0^2*n1)/(R^2*k2^2*n0^2 + R^2*n0^2*n2^2 + 2*R^2*n0*n1^2*n2 + R^2*n1^4 - k2^2*n0^2 - n0^2*n2^2 + 2*n0*n1^2*n2 - n1^4));
n_new_2 = -(pi*d1*n1)/atan((n1*(- R^4*k2^4*n0^2 - 2*R^4*k2^2*n0^3*n2 - 2*R^4*k2^2*n0^2*n1^2 - 2*R^4*k2^2*n0^2*n2^2 - 2*R^4*k2^2*n0*n1^2*n2 - R^4*n0^4*n2^2 - 2*R^4*n0^3*n1^2*n2 - 2*R^4*n0^3*n2^3 - R^4*n0^2*n1^4 - 4*R^4*n0^2*n1^2*n2^2 - R^4*n0^2*n2^4 - 2*R^4*n0*n1^4*n2 - 2*R^4*n0*n1^2*n2^3 - R^4*n1^4*n2^2 + 2*R^2*k2^4*n0^2 + 4*R^2*k2^2*n0^2*n1^2 + 4*R^2*k2^2*n0^2*n2^2 + 2*R^2*n0^4*n2^2 + 2*R^2*n0^2*n1^4 - 8*R^2*n0^2*n1^2*n2^2 + 2*R^2*n0^2*n2^4 + 2*R^2*n1^4*n2^2 - k2^4*n0^2 + 2*k2^2*n0^3*n2 - 2*k2^2*n0^2*n1^2 - 2*k2^2*n0^2*n2^2 + 2*k2^2*n0*n1^2*n2 - n0^4*n2^2 + 2*n0^3*n1^2*n2 + 2*n0^3*n2^3 - n0^2*n1^4 - 4*n0^2*n1^2*n2^2 - n0^2*n2^4 + 2*n0*n1^4*n2 + 2*n0*n1^2*n2^3 - n1^4*n2^2)^(1/2) + k2*n1^3 - k2*n0^2*n1 - R^2*k2*n1^3 + R^2*k2*n0^2*n1)/(R^2*k2^2*n0^2 + R^2*n0^2*n2^2 + 2*R^2*n0*n1^2*n2 + R^2*n1^4 - k2^2*n0^2 - n0^2*n2^2 + 2*n0*n1^2*n2 - n1^4));
n_new_3 = (pi*d1*n1)/atan((k2^2*n0*n1*1i - k2*n0^2*n1 + k2*n1^3 + n0^2*n1*n2*1i + n0*n1^3*1i + n0*n1*n2^2*1i + n1^3*n2*1i)/(k2^2*n0^2 + n0^2*n2^2 + 2*n0*n1^2*n2 + n1^4));
n_new_4 = -(pi*d1*n1)/atan((k2^2*n0*n1*1i + k2*n0^2*n1 - k2*n1^3 + n0^2*n1*n2*1i + n0*n1^3*1i + n0*n1*n2^2*1i + n1^3*n2*1i)/(k2^2*n0^2 + n0^2*n2^2 + 2*n0*n1^2*n2 + n1^4));
nd
fid=fopen('results_n_solve.csv','a');
fprintf(fid,'%5.5, %5.5, %5.5, %5.5f\n',n_new_1,n_new_2,n_new_3,n_new_4);
fclose(fid);
When I try to run this code, I get an error that reads:
Error in ==> n_iterations at 22
fprintf(fid,'%5.5, %5.5, %5.5,
%5.5f\n',n_new_1,n_new_2,n_new_3,n_new_4);
Error in ==> run at 74
evalin('caller',[script ';']);
Why am I getting this error? Isn't n_new_1 defined as the solutions above?

Walter Roberson on 21 Feb 2012
for n1 = [2:.01:1.5];
has its end point (1.5) greater than its start point (2), so it is never executed.
If you want a loop to count down, you must use a negative increment (e.g., -0.01) rather than a positive one.

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