How do I perform several iterations in MATLAB?

I am trying to find the corresponding wave length from about 8,000 wave period data points. I have the matlab code to import the data and turn it into a table. I need to use each individual wave period and run iterations to find wave length using this equation: L = 1.56(T^2)tanh(61.58/L). I am not sure where to start, this is all I have so far.

%% Create Table From Excel File
% Identify excel file
filename = '2022WaveData.xlsx'; % Excel File Name
sheet = 1; % Sheet number
% Import data from the Excel file
wavedata = readtable(filename);
% Select every 2nd cell from the data - create array of hourly data
hourlydata = wavedata(1:2:end, :); 
% Use only two columns from the selected data
hourlydata = hourlydata(:, 9:10); % Isolate wave height and dominant wave period
% Display the selected data
disp('Hourly Wave Data 2022:');
disp(hourlydata);
%% Perform an iterative calculation to find wavelength
% L = 1.56*(y^2)*tanh(61.58/L)
% Initial guess for L
L = 60; 
% Perform the iterative calculation
y = hourlydata(:, 2); 
for K = 1 : 100
    L = 1.56*(y^2)*tanh(61.58/L);
end
% Display the final value of L
disp(['The wavelength [m] is approximately: ', num2str(L)]);

Any help would be greatly appreciated!

Answer 1

[Star Strider]

Since ‘y’ appears to be a column vector, the loop is not necessary. Just use:

L = 1.56*(y.^2)*tanh(61.58/L);

If you are looping through various columns of ‘hourlydata’ the loop still is not necessary —

L = 60;
y = randn(10,5)

y = 10×5

0.7598 -0.4159 0.9938 0.3012 1.5481 0.1682 -0.9686 0.2074 -1.5123 1.4598 1.5901 0.5688 -0.9679 0.6580 -0.7723 1.0208 -0.4262 -0.2904 2.6653 0.8932 -1.3013 -0.1593 0.8142 -2.4869 1.3280 0.0064 -1.0026 1.1594 0.8647 1.2845 -1.5432 0.4921 0.3040 -0.8782 -1.4256 -1.0761 -0.2994 0.7769 1.8965 0.5642 1.6883 0.6276 -0.8931 0.4189 -1.5163 -0.3547 1.7922 0.4473 0.9087 0.5698

L = 1.56*(y.^2)*tanh(61.58/L)

L = 10×5

0.6957 0.2084 1.1902 0.1093 2.8878 0.0341 1.1305 0.0518 2.7558 2.5680 3.0467 0.3899 1.1288 0.5217 0.7187 1.2556 0.2189 0.1016 8.5603 0.9613 2.0405 0.0306 0.7988 7.4523 2.1250 0.0000 1.2112 1.6197 0.9010 1.9883 2.8696 0.2918 0.1114 0.9294 2.4491 1.3954 0.1080 0.7273 4.3341 0.3835 3.4347 0.4746 0.9611 0.2114 2.7706 0.1516 3.8705 0.2411 0.9949 0.3913

If there is something in your question that I am missing, please clarify.

.

[Alexis]

This worked thank you! First I had to use curly brackets to pull the wave periods (y) from the table using y=hourlydata{:, 2}; then it ran the iterations and gave me all my values for L. Thanks again!

[Star Strider]

As always, my pleasure!

Answer 2

[Walter Roberson]

Change

for K = 1 : 100
    L = 1.56*(y^2)*tanh(61.58/L);
end

to

LGuess = 60;
for K = 1 : 100
    L(K) = fzero(@(L) 1.56*(y(K)^2)*tanh(61.58/L) - L, LGuess);
end

This presumes that L = 1.56*(y^2)*tanh(61.58/L) is an equation to be solved for L given a particular y value.