Difficulty in extracting the particular variable value (a_mean, a_std) from the code

I want to fit an quadratic plateau equation and find the statistics of the parameters.

The form of equation are given as:

y=a*(x)^2+b*(x)+c, x < xc(Ymax)

y=yp, x >= xc(Ymax)

x=[0,40,80,100,120,150,170,200],

y=[1865,2855,3608,4057,4343,4389,4415,4478]

The code which I have tried for this purpose is given as:

function Fiting_ex()

global a_iter b_iter c_iter

a_iter = 0;

b_iter = 0;

c_iter = 0;

x=[0; 40; 80; 100; 120; 150; 170; 200];

y=[1865; 2855; 3608; 4057; 4343; 4389; 4415; 4478];

X = [x.^2 x ones(numel(x),1)];

A = y\X;

a0=A(1);

b0=A(2);

c0=A(3);

B0 = [a0; b0; c0];

[Bm,normresm] = fminsearch(@(b) myfun(b,x,y),B0);

a=Bm(1);

b=Bm(2);

c=Bm(3);

xc=-b/(2*a);

p=c-(b^2/(4*a));

yfit = zeros(numel(x),1);

for i=1:numel(x)

if (x(i) < xc)

yfit(i) = a.*x(i).^2+ b*x(i)+c;

else

yfit(i) = p;

end

end

plot(x,yfit,'*')

hold on;

plot(x,y);

hold off

% Statistic on optimization process

a_mean = mean(a_iter(2:end)); % mean value

a_var = var(a_iter(2:end)); % variance

a_std = std(a_iter(2:end)); % standard deviation

function f = myfun(Bm, x, y)

global a_iter b_iter c_iter

a_iter = [a_iter Bm(1)];

b_iter = [b_iter Bm(2)];

c_iter = [c_iter Bm(3)];

yf = Bm(1)*(x).^2+Bm(2)*(x)+Bm(3);

a=Bm(1);

b=Bm(2);

c=Bm(3);

xc=-b/(2*a);

p=c-(b^2/(4*a));

yfit = zeros(numel(x),1);

for i=1:numel(x)

if (x(i) < xc)

yfit(i) = a.*x(i).^2+ b*x(i)+c;

else

yfit(i) = p;

end

end

f = norm(y - yfit);

When I run this script, no error have shown in command window, but I am unable to get the values of the variables (a_mean, a_std, a_var, yfit), I mean it did not display the values of these variables. How can I extrat these value from this code.

I have another query related to the equation that if I want to repalce 'x' with 'x+n', where n is also a unknown parameter. Also I need to find the mean, standard deviation of this parameter (n) too. Then what will be the changes in above code.

Kindly help me for this...

[KALYAN ACHARJYA]

particular variable value

Which variable?

[madhuri dubey]

Kindly read the whole question I hope you will understand what I want to find or what is my difficulties.

Answer 1

[KALYAN ACHARJYA]

Answer of this question

When I run this script, no error have shown in command window, but I am unable to get the values of the variables (a_mean, a_std, a_var, yfit), I mean it did not display the values of these variables. How can I extract these value from this code.

Use the following at end of the code

fprintf('The value of a_mean is %.2f',a_mean);
fprintf('The value of a_std is %.2f',a_std);
fprintf('The value of yfit is %.2f',yfit);

Here %f represents floating number, for decimal you can use %d also in palce of %.2f

[madhuri dubey]

Thank you... And what about the second portion of my question i.e. what will be the changes in this code if I want to replace 'x' with 'x+n' in the equation (a*x^2+b*x+c) .