How to obtain a value from a program and replace in an equation?

Hello, everybody, i hope all of you have a wonderful day, my problem is this, i have this program, and from this program obtain this values of alpha from a series of data, this data obey this equation:

that are in function of the wind direction, but now, i want to obtain from this phormula the wind velocity but the alphas depend of the wind direction, so i have all, except the diferent type of alpha from every wind direction...

So if you can help me ... would be amazing. Thank you again.

Best!!

numData = xlsread('DireccionViento.xlsx');
alpha           = numData(:,2);
DireccionViento = numData(:,1);

paso = 30;
kstd = 2;

direcs = (0:paso:360)';
s = length(direcs);
alpha_prom = nan(s-1, 1); %not a number

for k=1:(s-1)
    
    MSKk = (DireccionViento>=direcs(k)) & (DireccionViento<=direcs(k+1));
    alpha_k = alpha(MSKk);
    
    % filtremos un poco antes del promedio
    stdk = nanstd(alpha_k);
    avek = nanmean(alpha_k);
    MSKstd = (alpha_k > avek - kstd*stdk)&(alpha_k < avek + kstd*stdk); % kstd desvios estándar
    alpha_msk = alpha_k(MSKstd);
    
    meank = nanmean(alpha_msk);
    alpha_prom(k) = meank;
    
    % grafico
    sk = length(alpha_k);
    xk = (1:1:sk);
    figure(k+1)
    plot(xk, alpha_k, '.-b'); hold on; %valores de alpha 
    plot(xk(MSKstd), alpha_msk, '*r'); %gráficas con desviación estandár  en rojo
    plot(xk, meank+0*xk, '-g'); hold on; %promedio de alpha 
    
end

x_direcs = direcs(1:s-1) + paso/2;

figure(1)
plot(x_direcs, alpha_prom, '*r') %grafica de alpha promedio con valores de grados 

[Image Analyst]

What are w1, w2, z1, and z2? I don't see them in your code. Can you use the same letters as the image so we know what is what?

Which variable in your code represents the velocity?

Sorry that I don't speak that language so I don't know what you're plotting. What do xk, alpha_k, alpha_msk, and meank represent? Is any of those velocity? Is xk time, distance, or something else? And in the third plot why are you multiplying the second term by 0? Because meank+0*xk is simply meank.

Can you attach the workbook so we can run your code?

[Ana Soph]

• What are w1, w2, z1, and z2? I don't see them in your code. Can you use the same letters as the image so we know what is what?

w1 = wind velocity of the station of 32 m

w2 = wind velocity of the station of 18 m (data that i need)

z1 = height 32 m

z2=height of 18 m

but i don't use it yet, because i have to obtain the alpha for every wind direction that i have and then replace it.

• Which variable in your code represents the velocity?

sorry, in my code i don't have wind velocity yet, because i don't know how to do that

• Sorry that I don't speak that language so I don't know what you're plotting. What do xk, alpha_k, alpha_msk, and meank represent? Is any of those velocity? Is xk time, distance, or something else?

It is totally fine, i understand, i am plotting the values of alpha, standar deviation and the mean of alpha for all the values, the first graph is only the wind direction (in the X axes(in degrees), and in the Y axes is the mean alpha for this values of wind direction) no any one of those are velocity, xk only is for plot the values of alpha.

• And in the third plot why are you multiplying the second term by 0? Because meank+0*xk is simply meank.

Yes, it is a trick, 0 * xk generates a vector of the same size as xk, but with zeros inside

[Ana Soph]

in this file i have in the first column the wind direction and in the second the wind velocity, this wind velocity is the wind velocity that i want to replace in the phormula for obtain the other wind velocity (18 meters)...

Best!

Answer 1

[Image Analyst]

Try this:

clc;    % Clear the command window.
fprintf('Beginning to run %s.m.\n', mfilename);
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;

numData = xlsread('DireccionVelocidadViento.xlsx');
alpha           = numData(:,2);
DireccionViento = numData(:,1);
% Plot the data.
hFig1 = figure;
hFig1.WindowState = 'maximized';
plot(alpha, DireccionViento, 'b*-');
grid on;
xlabel('alpha', 'FontSize', fontSize);
ylabel('DireccionViento', 'FontSize', fontSize);

paso = 30;
kstd = 2;
% Define parameters from the equation.
w1 = 10; % Whatever.
z1 = 32;
z2 = 18;

direcs = (0:paso:360)'
numberOfDireccions = length(direcs);
alpha_prom = nan(numberOfDireccions-1, 1); %not a number
hFig2 = figure;
hFig2.WindowState = 'maximized';
for k = 1 : (numberOfDireccions-1)    
	% Find all indexes more than 0 but less than 30, or more than 30 but less than 60, etc. and is not nan.
    validIndexes = (DireccionViento>=direcs(k)) & (DireccionViento<=direcs(k+1)) & ~isnan(DireccionViento); % A vector
	% Get the alpha's for those indexes.
    alpha_k = alpha(validIndexes); % A vector.
    
    % filtremos un poco antes del promedio
	% Get the mean and std dev of the alpha's for those directions.
    stdk = nanstd(alpha_k); % A single scalar value.
    avek = nanmean(alpha_k); % A single scalar value.
	
	% Ignore outliers and find inliers - those points within +/- 2 standard deviations of the mean.
    inlierIndexes = (alpha_k > avek - kstd*stdk)&(alpha_k < avek + kstd*stdk); % kstd desvios estándar
    inlierAlphas = alpha_k(inlierIndexes);
    
	% Recompute the mean, now that we're ignoring outliers.
    meanInlierAlpha = nanmean(inlierAlphas); % A single scalar value.
    alpha_prom(k) = meanInlierAlpha;
    
	% Plot the alphas and mean alpha for this direction range.
    % grafico
    sk = length(alpha_k);
    xk = (1:1:sk);
    subplot(4, 4, k)
	% Plot the alphas for this direction range with a blue dot and lines connecting them.
    plot(xk, alpha_k, '.-b');  %valores de alpha 
	hold on; % Don't blow away other plots to come.
	% Plot the alphas for this direction range with a red star.
    plot(xk(inlierIndexes), inlierAlphas, '*r'); %gráficas con desviación estandár  en rojo
	% Plot a line across at the mean alpha for this range of directions.
    yline(meanInlierAlpha, 'Color', 'g', 'LineWidth', 2);  %promedio de alpha   
	legend('alpha', 'inlierAlphas', 'meanInlierAlpha', 'Interpreter', 'none');
	caption = sprintf('Direction = %d to %d', direcs(k), direcs(k+1));
	title(caption);
	xlabel('Index');
	grid on;
	drawnow;
	
	% Get the wind velocity for this mean alpha and for this range of directions.
	w2(k) = w1 / (z1/z2)^meanInlierAlpha;
end

x_direcs = direcs(1:numberOfDireccions-1) + paso/2;

% Plot alpha as function of direccion.
subplot(4, 4, 13:14);
plot(x_direcs, alpha_prom, 'r*-', 'LineWidth', 2) %grafica de alpha promedio con valores de grados 
grid on;
title('Alpha as function of Direccion', 'Interpreter', 'none');
xlabel('x_direcs', 'FontSize', fontSize, 'Interpreter', 'none');
ylabel('alpha_prom', 'FontSize', fontSize, 'Interpreter', 'none');

% Plot velocity as function of direccion.
subplot(4, 4, 15:16);
plot(x_direcs, w2, 'r*-', 'LineWidth', 2) %grafica de alpha promedio con valores de grados 
grid on;
title('w2 (velocity) as function of Direccion', 'Interpreter', 'none');
xlabel('x_direcs', 'FontSize', fontSize, 'Interpreter', 'none');
ylabel('w2 (Velocity)', 'FontSize', fontSize, 'Interpreter', 'none');

fprintf('Done running %s.m.\n', mfilename);

[Ana Soph]

thanks man <3

Answer 2

[Image Analyst]

Make 2 vectors then call polyfit().

direccion = 15 : 30 : 345;
alphas = [0.62, etc.
% Fit to a quadratic or whatever you want.
coefficients = polyfit(direccion, alphas, 2);
% Get fitted values
alphaFitted = polyval(coefficients, direccion);
plot(direccion, alphas, 'b.', 'LineWIdth', 2, 'MarkerSize', 20);
hold on;
plot(direccion, alphaFitted, 'r-', 'LineWIdth', 2);
grid on;

[Ana Soph]

Thanks but, i want with the wind direction and alphas obtain the wind velocity (w1) that is obtained with the alphas but the alphas where obtained with help of the program below that is correspondent with wind direction. I hope i was clear

[Ana Soph]

for example , this is what happen with your program, doesn't fit well, but ok, doesn't matter, i have the phormula, and i want the wind velocity that depends of wind direction, because every alpha is for a respective value of wind direction, but in the phormula i want to substitute the alpha that would correspond to that wind direction

Seriously, thank you for your valious time,I hope you can help me

[Image Analyst]

OK, I can help but you keep forgetting to attach 'DireccionViento.xlsx'. I have no idea what's in it. Does it just contain the table you showed a picture of? If so, why not attach the workbook and save me the trouble of having to type in hundreds of numbers?

[Ana Soph]

ok, i am sorry , is true, here I attach the corresponding document

Thanks a lot !

[Ana Soph]

the height of the values are 32m, the height of the new station is 18m (this is the value that i need) , i have the other months if you need .

Best!!