Iterating an array in a for loop

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laura byrne 2021-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/752539-iterating-an-array-in-a-for-loop

编辑： KALYAN ACHARJYA 2021-2-22

Hi I want to iterate an array in a for loop but within a while loop if this makes sense. Im trying to set the condition where while the value of diameter is less than that of final diameter, the loop executes code which is stored in an empty array but I'm not sure how to do this. I'm trying to set up the for loop so that it executes until the array is filled ie until the values of diameter reach the value of diameter final? Thanks in advance for your help :-)

focal_length = 50e-02;
m = 1;
diameter = 0.5e-03
diameter_final = 6e-03;
wavelength = 450e-06
diameter_a = {}
wavelength_a = {}
while diameter <= diameter_final
    for size(diameter_a{}) < 1:6
    theta = atand(diameter/focal_length);
    d = (m*wavelength/sin(theta));
    spatial_freq = 1/d
   
    
    diameter_a = diameter + 0.5e-03
    wavelength_a = wavelength + 5e-05
    plot(diameter_a, spatial_freq,"r,--*")
    ylabel("Spatial frequency (lines/mm)")
    hold on
    plot(wavelength_a,spatial_freq,"k")
    end
    
end

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Answer 1

KALYAN ACHARJYA 2021-2-22

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/752539-iterating-an-array-in-a-for-loop#answer_629959

编辑：KALYAN ACHARJYA 2021-2-22

在 MATLAB Online 中打开

You can avoid loop here

focal_length = 50e-02;
m = 1;
diameter=0.5e-03:0.5e-03:6e-03;
%% Create the Wavelength Array with Same dimension as diameter 
% Withn Given Intial value and step size
wavelength_int=450e-06;
wavelength_step=5e-05;
wavelength=wavelength_int+(1:length(diameter))*wavelength_step;
%% 
theta=atand(diameter/focal_length);
d=(m*wavelength)./sin(theta);
spatial_freq=1./d;
figure, plot(diameter, spatial_freq,'-*r');
ylabel("Spatial frequency (lines/mm)")
figure, plot(wavelength,spatial_freq,'k');
ylabel("Spatial frequency (lines/mm)")
grid on;
axis tight;

Kindly Do Verify

Note: y data are same for both plots, but x data are different. More you ca plots the data in multiple ways. Please refer MATLAB Docs

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laura byrne 2021-2-22

this works yes but the point of the exercise is to create a blank array and then use a loop to fill it

KALYAN ACHARJYA 2021-2-22

编辑：KALYAN ACHARJYA 2021-2-22

在 MATLAB Online 中打开

Not suitable for the case

Diameter present Value 
Wavelength present Value 
while to diameter <=some value  Check
calculate spatial_freq based on Diameter present Value & Wavelength present Value 
Store spatial_freq; % Plot Variable
Update Diameter 
Update Wavelength 
Store Updated Diameter & Wavelength % Plot variables
end

Here the diameter data is always one step ahead to check the condition, so its vector size is 1 element larger than spatial_freq and wavelength. The wavelength is updated even after the diameter update (although you can enter a break statement after the diameter update assignment to avoid the extra wavelength data).

Hence in the final plot, I have ignored the last elements of diameter and wavelength. More: Exact preallocation of the array data is not possible here, as we have no idea about the number of iterations (Disadvantage).

focal_length = 50e-02;
m = 1;
spatial_freq=[];
wavelength=[];
wavelength(1)=450e-06;
diameter=[];
diameter(1)=0.5e-03;
i=1;
while diameter<=6e-03
theta=atand(diameter(i)/focal_length);
d=(m*wavelength(i))/sin(theta);
spatial_freq(i)=1/d;
diameter(i+1)=diameter(i)+0.5e-03;
wavelength(i+1)=wavelength(i)+5e-05;
i=i+1;
end 
figure, plot(diameter(1:end-1),spatial_freq,'-*r');
ylabel("Spatial frequency (lines/mm)")
grid on;
figure, plot(wavelength(1:end-1),spatial_freq,'k');
ylabel("Spatial frequency (lines/mm)")
grid on;