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plotting and for loop

Asked by Ammar Ahmed on 12 Jun 2019
Latest activity Commented on by Ammar Ahmed on 14 Jun 2019
I'm plotting this function and the plotted line is blocky not smooth line. i want the line connecting the four input points become smoothy. without using the all point between them. Points are (0.20,0.23,0.25,0.27) linspace( x,y ) command generate all points and connected it , I'm trying using For loop to generate the plotting but it doesn't workout!!! any suggested command
the function
function F =P
P= [0.20,0.23,0.25,0.27];
e1=(1+1.8*10^14*1i);
e2=(2.5+2.5*10^-3*1i);
Hc=(10^6);
H1=(0);
Pc=(0.33).*exp((-abs(H1)/Hc));
c1=(1-3*Pc).*(((P)./(Pc)).^Pc).*(((1-P)./(1-Pc)).^(1-Pc));
F=(1./(2.*(2+c1))).*(((3*P-1+c1)*e1+(2-3.*P-c1)*e2)+(((((3*P-1+c1)*e1+(2-3.*P)*e2).^2)+(4.*(e1).*(e2).*(1-c1).*(2+c1))).^0.5));
plot(P,real(F))
title('Loss'),xlabel('(P)pressure '),ylabel('Force')
legend('<H>=0')
end

  2 Comments

Image Analyst
on 13 Jun 2019
Why are you assigning P ( the function name) to a 4 element vector inside the function itself? Is that even allowed? You should pick different names for the function and the variable.
Ammar Ahmed on 14 Jun 2019
thanks for the comment , it was mistakenly assigned.
how about my question it is possible to have smooth line plot using for loop command !! could please help me with your suggestion

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2 Answers

Walter Roberson
Answer by Walter Roberson
on 12 Jun 2019

You can generate a smooth curve between four points by doing interpolation, such as spline or pchip or makima ,
However, looking at your expression it is obvious that any attempt to do that would not give good results.
function F =P
P0= [0.20,0.23,0.25,0.27];
P = linspace(0.20, 0.27);
e1=(1+1.8*10^14*1i);
e2=(2.5+2.5*10^-3*1i);
Hc=(10^6);
H1=(0);
Pc=(0.33).*exp((-abs(H1)/Hc));
F = calc_f(P, Pc, e1, e2);
F0 = calc_f(P0, Pc, e1, e2);
Fint = interp1(P0, F0, P, 'spline');
subplot(1,2,1)
plot(P, real(F), 'k', P0, real(F0), 'b', P, real(Fint), 'r--')
title('Loss'),xlabel('(P)pressure '),ylabel('Force')
legend({'continuous', 'pointwise', 'interpolated'})
subplot(1,2,2)
plot(P, real(F)-real(Fint))
legend('continuous minus interpolated')
end
function F = calc_f(P, Pc, e1, e2);
c1=(1-3*Pc).*(((P)./(Pc)).^Pc).*(((1-P)./(1-Pc)).^(1-Pc));
F=(1./(2.*(2+c1))).*(((3*P-1+c1)*e1+(2-3.*P-c1)*e2)+(((((3*P-1+c1)*e1+(2-3.*P)*e2).^2)+(4.*(e1).*(e2).*(1-c1).*(2+c1))).^0.5));
end

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Answer by Ammar Ahmed on 13 Jun 2019

thanks for answering but as i see still i need to use P = linspace(0.20, 0.27); command which resulting in counting all points in between [0.20 , 0.27]
Does for loop command applicable to generate smooth line between the points
i need just the four point [0.20,0.23,025,0.27] connect in smooth line between them

  2 Comments

Walter Roberson
on 13 Jun 2019
You missed the point. I plot three different ways: your original four points, a fine grid, and spline interpolation. Then I plot the differences between the fine grid and the interpolation and show that interpolation does not do a good job.
MATLAB does not have a graphics primitive to input a few points and have it drawn a smooth curve. Any routine for that task would need to use interpretation. Which I show is not all that accurate.
Ammar Ahmed on 14 Jun 2019
thanks walter for your assisstant

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