How to find area enclosed between two curves?

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Prakash Chettri
Prakash Chettri 2022 年 2 月 21 日
回答済み: Torsten 2022 年 2 月 22 日
Lx = 150;
Ly = 150;
T0 =0;
T1 = pi/4;
T=3.175;
N=8;
W=N*T;
X0=Lx/2;
Y0=0;
W_nominal=W/2;
for a=1:2
r=rem(a,2);
if r==0
xp=0; xn=0; i=1;
while (xp>=0 && xp<=Lx/2)
XPaxisl(i)=xp+(i-1)*Lx/1200; xp=XPaxisl(i);
XNaxisl(i)=xn+(i-1)*(-Lx)/1200; xn=XNaxisl(i);
Th(i)=T0+2*((T1-T0)*(XPaxisl(i)))/Lx;
TH(i)= T0+2*((T0-T1)*(XNaxisl(i)))/Lx;
Wp(i)=W_nominal/cos(Th(i));
WP(i)=W_nominal/cos(TH(i));
ypl(i)=Wp(i)+(Lx/(2*(T0-T1))*((-log(cos(T0)))+log(cos(T0+((2*(T1-T0)*XPaxisl(i))/Lx)))));
ynl(i)=WP(i)+(Lx/(2*(T1-T0))*((-log(cos(T0)))+log(cos(T0+((2*(T0-T1)*XNaxisl(i))/Lx)))));
i=i+1;
end
plot(XPaxisl,ypl, '-g')
hold on
plot(XNaxisl,ynl, '-g')
hold on
end
%% shifting
r=rem(a,2);
if r==0
xp=0; xn=0; i=1; y=0; yn=0;
while (xp>=0 && xp<=Lx/2) && (y<=Ly/2)
XPaxiss1(i)=xp+(i-1)*Lx/1200; xp=XPaxiss1(i);
yps1(i) =(a*W_nominal)+Lx/(2*(T0-T1))*((-log(cos(T0)))+log(cos(T0+((2*(T1-T0)*XPaxiss1(i))/Lx))));
i=i+1;
end
else
xp=0; xn=0; i=1; y=0; yn=0;
while (xp>=0 && xp<=Lx/2) && (y<=Ly/2)
XPaxiss1(i)=xp+(i-1)*Lx/1200; xp=XPaxiss1(i);
XNaxiss1(i)=xn+(i-1)*(-Lx)/1200; xn=XNaxiss1(i);
yps1(i) =(a*W_nominal)+Lx/(2*(T0-T1))*((-log(cos(T0)))+log(cos(T0+((2*(T1-T0)*XPaxiss1(i))/Lx))));
yns1(i)= (a*W_nominal)+Lx/(2*(T1-T0))*((-log(cos(T0)))+log(cos(T0+((2*(T0-T1)*XNaxiss1(i))/Lx))));
i=i+1;
end
plot(XPaxiss1,yps1, '-r')
hold on
plot(XNaxiss1,yns1, '-r')
xlim([-Lx/2 Lx/2])
ylim([-Ly/2 Ly/2])
end
end
I want to claculate the area between red and green curves using trapz but im not getting the exact result and it is showing error while calculating.can anyone tell how can i calculate area? I attached code for reference.

採用された回答

Torsten
Torsten 2022 年 2 月 22 日
Lx = 150;
Ly = 150;
T0 =0;
T1 = pi/4;
T=3.175;
N=8;
W=N*T;
X0=Lx/2;
Y0=0;
W_nominal=W/2;
for a=1:2
r=rem(a,2);
if r==0
xp=0; xn=0; i=1;
while (xp>=0 && xp<=Lx/2)
XPaxisl(i)=xp+(i-1)*Lx/1200; xp=XPaxisl(i);
XNaxisl(i)=xn+(i-1)*(-Lx)/1200; xn=XNaxisl(i);
Th(i)=T0+2*((T1-T0)*(XPaxisl(i)))/Lx;
TH(i)= T0+2*((T0-T1)*(XNaxisl(i)))/Lx;
Wp(i)=W_nominal/cos(Th(i));
WP(i)=W_nominal/cos(TH(i));
ypl(i)=Wp(i)+(Lx/(2*(T0-T1))*((-log(cos(T0)))+log(cos(T0+((2*(T1-T0)*XPaxisl(i))/Lx)))));
ynl(i)=WP(i)+(Lx/(2*(T1-T0))*((-log(cos(T0)))+log(cos(T0+((2*(T0-T1)*XNaxisl(i))/Lx)))));
i=i+1;
end
%figure(1)
plot(XPaxisl,ypl, '-g')
hold on
plot(XNaxisl,ynl, '-g')
hold on
x1 = XPaxisl;
y1 = ypl;
x2 = XNaxisl;
y2 = ynl;
end
%% shifting
r=rem(a,2);
if r==0
xp=0; xn=0; i=1; y=0; yn=0;
while (xp>=0 && xp<=Lx/2) && (y<=Ly/2)
XPaxiss1(i)=xp+(i-1)*Lx/1200; xp=XPaxiss1(i);
yps1(i) =(a*W_nominal)+Lx/(2*(T0-T1))*((-log(cos(T0)))+log(cos(T0+((2*(T1-T0)*XPaxiss1(i))/Lx))));
i=i+1;
end
else
xp=0; xn=0; i=1; y=0; yn=0;
while (xp>=0 && xp<=Lx/2) && (y<=Ly/2)
XPaxiss1(i)=xp+(i-1)*Lx/1200; xp=XPaxiss1(i);
XNaxiss1(i)=xn+(i-1)*(-Lx)/1200; xn=XNaxiss1(i);
yps1(i) =(a*W_nominal)+Lx/(2*(T0-T1))*((-log(cos(T0)))+log(cos(T0+((2*(T1-T0)*XPaxiss1(i))/Lx))));
yns1(i)= (a*W_nominal)+Lx/(2*(T1-T0))*((-log(cos(T0)))+log(cos(T0+((2*(T0-T1)*XNaxiss1(i))/Lx))));
i=i+1;
end
plot(XPaxiss1,yps1, '-r')
hold on
plot(XNaxiss1,yns1, '-r')
xlim([-Lx/2 Lx/2])
ylim([-Ly/2 Ly/2])
x3 = XPaxiss1;
y3 = yps1;
x4 = XNaxiss1;
y4 = yns1;
end
end
x2=x2(end:-1:1);
y2=y2(end:-1:1);
x4=x4(end:-1:1);
y4=y4(end:-1:1);
X1 = horzcat(x2(1:end-1),x1)
Y1 = horzcat(y2(1:end-1),y1);
X2 = horzcat(x4(1:end-1),x3)
Y2 = horzcat(y4(1:end-1),y3);
%figure(2)
%plot(X1,Y1)
%hold on
%plot(X2,Y2)
%xlim([-Lx/2 Lx/2])
%ylim([-Ly/2 Ly/2])
Area = trapz(X1,abs(Y1-Y2))

その他の回答 (1 件)

Abolfazl Chaman Motlagh
Abolfazl Chaman Motlagh 2022 年 2 月 21 日
i don't think the code you include in your question content related to what you want.
you have to vector, which are values of your curves at your grid points x.
here's an example for doing this task:
x = 0:0.1:20;
y1 = exp(x/2);
y2 = (x).^3;
dY = abs(y1-y2);
plot(x,y1,'Color','r','LineWidth',2);
hold on; grid on;
plot(x,y2,'Color','g','LineWidth',2);
plot(x,dY,'Color','b','LineWidth',2);
legend('y1 = exp(x/2)','y2= x^3','|y1-y2|','Location','best');
Diff = trapz(x,dY);
disp(['Area between 2 Curves :' num2str(Diff)])
Area between 2 Curves :26164.3149
  1 件のコメント
Prakash Chettri
Prakash Chettri 2022 年 2 月 22 日
Thank you for the help. But i want to calculate area between curve given by "ypl(i)" and "yps1(i)" over x domain as XPaxisl(i) as noted in a code attached by me.

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