plotting and for loop

Question

Ammar Ahmed 2019-6-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/466800-plotting-and-for-loop

评论： Ammar Ahmed 2019-6-14

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

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Image Analyst 2019-6-13

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 2019-6-14

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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Answer 1

Walter Roberson 2019-6-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/466800-plotting-and-for-loop#answer_378948

在 MATLAB Online 中打开

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 2

Ammar Ahmed 2019-6-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/466800-plotting-and-for-loop#answer_378990

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

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Walter Roberson 2019-6-13

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 2019-6-14