MATLAB: Fitting every fifth datapoint one after another

poly1 data analysis

Hello!

I want to do a linear regression for a bunch of data, using every fifth or third (maybe tenth) Datapoint. The data will be vary in size and therefor I need to do a function that varies as well.

I did the poly1-fit to the first 13 data already by typing it for each fit. Can you think of any way to solve it via function maybe a loop to solve this seccessively for any size of x- or y-datapoints.

I will be happy for any kind of response that helps me to solve this problem.

Thanks a lot!

The result should look like this for more datapoints:

Best Answer

I have a solution that avoids the loops altogehter, but might not be as readable

n = 5; % Number of datapoints
x1 = reshape(x, n, []); % please make sure, that your number will be divisable into n Elements
y1 = reshape(y, n, []);
a = (x1-x1(1,:))\(y1-y1(1,:)); % we use mldivide here and correct for the origin
a = a(1,:);
b = y1(1,:) - a.*x1(1,:); % here we shifted back

b is the offset and a the slope of your curves

Related Solutions

MATLAB: Using fsolve over a range of equations.

Solve the equations once and then plug in the values.

for z = 100:105
  x1=velprof(z,y1);
  x2=velprof(z,y2);
  x3=velprof(z,y3);
  x4=velprof(z,y4);
  c = [ (((x3*y4-x4*y3)*x2^2+(-x3^2*y4+x4^2*y3)*x2+x3*x4*y2*(-x4+x3))*x1^3+((-x3*y4+x4*y3)*x2^3+(-x4^3*y3+x3^3*y4)*x2+y2*x3*x4^3-x3^3*x4*y2)*x1^2+((x3^2*y4-x4^2*y3)*x2^3+(x4^3*y3-x3^3*y4)*x2^2+x3^2*x4^2*y2*(-x4+x3))*x1-x3*x2*x4*y1*(-x4+x3)*(x2-x4)*(x2-x3))/((-x4+x3)*(x2-x4)*(x2-x3)*(x1-x4)*(x1-x3)*(x1-x2)), ...
  (((-y2+y1)*x4^2+(y2-y4)*x1^2-x2^2*(y1-y4))*x3^3+((-y1+y2)*x4^3+(y4-y2)*x1^3+x2^3*(y1-y4))*x3^2+((y3-y2)*x1^2+x2^2*(y1-y3))*x4^3+((y2-y3)*x1^3-x2^3*(y1-y3))*x4^2+x1^2*x2^2*(y3-y4)*(x1-x2))/((-x4+x3)*(x2-x4)*(x2-x3)*(x1-x4)*(x1-x3)*(x1-x2)), ...
  (((y4-y3)*x2+(y2-y4)*x3-x4*(y2-y3))*x1^3+((y3-y4)*x2^3+(y4-y2)*x3^3+x4^3*(y2-y3))*x1+((-y1+y4)*x3+x4*(y1-y3))*x2^3+((y1-y4)*x3^3-x4^3*(y1-y3))*x2-x3*x4*(-x4+x3)*(x3+x4)*(-y2+y1))/((-x4+x3)*(x2-x4)*(x2-x3)*(x1-x4)*(x1-x3)*(x1-x2)), ...
  (((y3-y4)*x2+(y4-y2)*x3+x4*(y2-y3))*x1^2+((y4-y3)*x2^2+(y2-y4)*x3^2-x4^2*(y2-y3))*x1+((y1-y4)*x3-x4*(y1-y3))*x2^2+((-y1+y4)*x3^2+x4^2*(y1-y3))*x2+x3*x4*(-y2+y1)*(-x4+x3))/((-x4+x3)*(x2-x4)*(x2-x3)*(x1-x4)*(x1-x3)*(x1-x2)) ];
  disp(z)
  disp(c)
end

MATLAB: If I have a plotted curve with a small gap in the midlle, how can I fill the gap with a straight line

I have no idea what your curve is or the reason the gap exists, so this is a guess. The approach to both is to find the ends of the first part of the curve, and connect them to the beginning of the second part.

If you know where the gap is, try this:

x1 = linspace(0, 1);
y1 = sin(x1*3*pi);
x2 = x1 + 2;
y2 = cos(x2*4*pi);
figure
subplot(2,1,1)
plot(x1, y1, 'g')
hold on
plot(x2, y2, 'g')
hold off
subplot(2,1,2)
plot(x1, y1, 'g')
hold on
plot(x2, y2, 'g')
plot([x1(end) x2(1)], [y1(end) y2(1)], '-r')                            % Connect Ends With Red Line

hold off

If your data have a region of one or more consecutive NaN values, try this:

x3 = linspace(0, 5);
x3(40:60) = NaN;
y3 = exp(-(x3-2.5).^2);
nanv = find(isnan(y3));                                                 % Find Region With ‘NaN’ Values
figure
plot(x3, y3, 'g')
hold on
plot(x3([nanv(1)-1, nanv(end)+1]), y3([nanv(1)-1, nanv(end)+1]), 'r')   % Connect Ends With Red Line
hold off

Best Answer

Related Solutions

MATLAB: Using fsolve over a range of equations.

MATLAB: If I have a plotted curve with a small gap in the midlle, how can I fill the gap with a straight line

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