how to find ascending and descending of hysteresis loop?

I had ploted tow vectors: current=[........]; flux=[.........], which is hysteresis loop. plot(current,flux) I want to find the ascending and descending points in loop. note: see the attachement

Answer 1

[Star Strider]

This code:

s = load('Zaid_20140517.mat')
x = s.current;
y = s.flux;
z = linspace(min(x),max(x),length(x))

[cmin,cxix] = (min(x))
[cmax,cnix] = (max(x))

[fmin,fxix] = (min(y))
[fmax,fnix] = (max(y))

figure(1)
plot(x, y)
hold on
plot([cmin  cmax],  [fmin  fmax], '+r', 'MarkerSize', 5, 'LineWidth',1.5)
hold off
grid
text(cmin-0.2,fmin-0.02, sprintf('(%.3f, %.3f)',cmin, fmin), 'FontSize',8, 'FontName', 'Consolas', 'FontWeight', 'bold')
text(cmax-0.4,fmax+0.02, sprintf('(%.3f, %.3f)',cmax, fmax), 'FontSize',8, 'FontName', 'Consolas', 'FontWeight', 'bold')

produces this plot:

[zaid]

thank you for very helpful answer. the answer is not what i mean but it has very good code that i need it, however,as you know the loop is increasing from minimum negative value up to zero then from zero to maximum positive value, this is ascending points or curve, then start to decrease from maximum value to zero, then from zero to minimum negative value again to make a loop, and this is called descending points or curve. so could you please help me how to find these tow curves (ascending and descending?

[Star Strider]

I found a paper on modeling hysteresis that I used to fit the equations.

This works:

Phi1 = @(b,I) -(b(1) .* atan(-b(2)*I+b(3)) - b(1).*I.*b(4));    % Descending
Phi2 = @(b,I)  (b(1) .* atan(-b(2)*I+b(3)) + b(1).*I.*b(4));    % Ascending

ixd = fix(length(x)/2);
vi2 = 1:ixd;
vi1 = ixd:length(x);

opts = statset('MaxIter', 5000, 'MaxFunEvals', 10000);
B1 = nlinfit(x(vi1), y(vi1), Phi1, ones(4,1),  opts );
B2 = nlinfit(x(vi2), y(vi2), Phi2, ones(4,1),  opts );

FitPhi1 = Phi1(B1,x);
FitPhi2 = Phi2(B2,x);

figure(1)
plot(x(vi1), y(vi1), x, FitPhi1, '-r', 'LineWidth', 2)
hold on
plot(x(vi2), y(vi2), x, FitPhi2, '-g', 'LineWidth', 2)
hold off
grid
legend('Data', 'Descending', 'Ascending', 'Location', 'NW')

producing this plot:

The ‘Ascending’ is green. MATLAB glitched in the legend.

The estimated parameters for the descending are:

B1 =

     253.0176e-003
      12.5475e+000
      -2.2488e+000
     176.5498e-003

and for the ascending:

B2 =

     246.5556e-003
     -12.7726e+000
      -2.4544e+000
     224.5136e-003

I will leave you to make sense of them. This is not an area of my expertise.

[zaid]

thank you very much.

[Star Strider]

Again, my pleasure!