I am trying to plot the real part and imaginary part graph using bvp4c and I am getting a straight line,

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Syed Mohiuddin 2023-1-1

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https://ww2.mathworks.cn/matlabcentral/answers/1886962-i-am-trying-to-plot-the-real-part-and-imaginary-part-graph-using-bvp4c-and-i-am-getting-a-straight-l

编辑： Cris LaPierre 2023-1-10

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I have a coupled non-linear differential equations

(d^2 f)/(dy^2 )+m2*g2*dB/dy-2*i*R2*g1*f - g3*G1*y - R4*g1 = 0

(d^2 B)/(dy^2 )+t4/(1-i*H1)*df/dy=0

Boundary conditions are

f=0 at y=0

f=C1 at y=1

And

dB/dy-(t4/(P1* (1-i*H1 ) ))* B=0 at y=0

dB/dy+(t4/(P2 (1-i*H1 ) ))* B=0 at y=1

Matlab programs

close all

clc

p=1;

P1=2;

P2=2;

b1=0.00021;

b2=0.000058;

S1=0.005;

S2=580000;

G1=2;

m2=20;

R1=997.1;

R2=3;

C1=1;

R3=4420;

B=0.5;

H1=0.25;

K1=3;

R4=1;

t1=(1./((1-p).^2.5));

t2=(1-p)+(p.*(R3./R1));

t3=(1-p)+p.*((R3.*b2)./(R1.*b1));

S=(S2./S1);

t4=1-((3*(1-S).*p)./((2+S)+(1-S).*p));

g1=t2./t1;

g2=1/t1;

g3=t3./t1;

m1=(t4./(P1.*(1-1i.*H1)));

m2=(t4./(P2.*(1-1i.*H1)));

dydx=@(x,y)[y(3);

y(4);

-m2.*g2.*y(4)+2.*1i.*R2.*g1.*y(1)+g3.*G1.*x+R4.*g1;

(-t4./(1-1i.*H1)).*y(3)];

BC = @(ya,yb)[ya(1);yb(1)-C1;ya(4)-m1.*ya(2);yb(4)+m2.*yb(2)];

yinit = [0.01;0.01;0.01;0.01];

solinit = bvpinit(linspace(0,1,50),yinit);

U1 = bvp4c(dydx,BC,solinit);

hold on

plot(U1.x,real(U1.y(1,:)),'r','linewidth',1.5)

plot(U1.x,imag(U1.y(1,:)),'b','linewidth',1.5)

I am trying to plot the real part and complex part graph and I am getting a straight line, I have checked the program and it seems good, but the type of graph I need to get is not appearing, I think the bvp4c code I have written might be wrong. Please help me. The graph I have to get should be of the form. Thank you