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我需要在matlab中使用ODE45解决这个二阶方程组我只熟悉使用ODE45可能有一个或两个方程但不是这么多这是我所拥有的，但我不知道如何纠正它：

function second_oder_ode

t = 0:0.001:3;   % time scale
theta = pi/2;
phi = 0;

initial_t    = 0;
initial_dtds = 0;
initial_r    = 0;
initial_drds = 0;
initial_theta    = 0;
initial_dthetads = 0;
initial_phi    = 0;
initial_dphids = 0;

[t,x] = ode45( @(t,y) rhs(t,y,theta,phi), t, [initial_t initial_dtds initial_r initial_drds initial_theta initial_dthetads initial_phi initial_dphids] );

plot(t,x(:,1));
xlabel('t'); ylabel('r');
%%%%%%%%%%%%%% STATE VECTORS %%%%%%%%%%%%%%%%%%%%%
t = [t, dtds];
r = [r, drds];
theta = [theta, dthetads];
phi = [phi, dphids];
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function dxds=rhs(t,r, theta, phi)
    dxds_1 = t(2);
    dxds_2 = -((2/3)*R0^(2)*((3*H0/(2*cv))^(4/3))*y(1)^(1/3))*(y(4)^(2)+abs(y(3))^(2)*y(6)^(2)+abs(y(3))^(2)*(sin(y(5)))^(2)*y(8)^(2));
    dxds_3 = r(2);
    dxds_4 = -(4/(3*y(1)))*y(2)*y(4)+abs(y(3))*(y(6)^(2)+(sin(y(5)))^(2)*y(8)^(2));
    dxds_5 = theta(2);
    dxds_6 = -(2/abs(y(3)))*y(4)*y(6)-(4/(3*y(1)))*y(2)*y(6)+((sin(2*y(5)))*(y(8)^(2))/2);
    dxds_7 = phi(2);
    dxds_8 = -2*y(8)*((2/(3*y(1)))*y(2)+(cot(y(5)))*y(6)+(1/abs(y(3)))*y(4));

    dxdt=[dxdt_1; dxdt_2; dxdt_3; dxdt_4; dxdt_5; dxdt_6; dxdt_7; dxdt_8];

   end
end
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1 回答 1

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这不是一个完整的解决方案，但比评论更长。

您似乎正在使用t thetaandphi每个用于两个目的。例如，可能将时间刻度线更改为使用s.

看看你的 odefun，这里叫做rhs，我认为它应该有 2 个参数。第一个参数应该是s（即使它没有被使用），第二个参数应该是一个向量输入，其中的值y(1:8)对应于[t; t_s; r; r_s; theta; theta_s; phi; phi_s]。

for 的表达式dxds_#应该只包含y和 no t、或r的术语。thetaphi

dxdt=您在应该包含dxds术语的行上有错别字。

下面我做了一些改变。我没有测试过这个；我没有常量R0，H0或者cv我认为它将统一为零。

我还删除了第一次出现的thetaand phi。我不确定这些应该如何在rhs.

function second_oder_ode

s = 0:0.001:3;   % time scale
%theta = pi/2;
%phi = 0;

initial_t    = 0;
initial_dtds = 0;
initial_r    = 0;
initial_drds = 0;
initial_theta    = 0;
initial_dthetads = 0;
initial_phi    = 0;
initial_dphids = 0;

y0 = [initial_t, initial_dtds, initial_r, initial_drds, ...
      initial_theta, initial_dthetads, initial_phi, initial_dphids];

[s,x] = ode45( @(s,y) rhs(s,y), s, y0);

plot(s,x(:,1));
xlabel('s'); ylabel('t(s)');
%%%%%%%%%%%%%% STATE VECTORS %%%%%%%%%%%%%%%%%%%%%
%t = [t, dtds];
%r = [r, drds];
%theta = [theta, dthetads];
%phi = [phi, dphids];
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function dxds=rhs(s,y)
    dxds_1 = y(2);
    dxds_2 = -((2/3)*R0^(2)*((3*H0/(2*cv))^(4/3))*y(1)^(1/3))*(y(4)^(2)+abs(y(3))^(2)*y(6)^(2)+abs(y(3))^(2)*(sin(y(5)))^(2)*y(8)^(2));
    dxds_3 = y(4);
    dxds_4 = -(4/(3*y(1)))*y(2)*y(4)+abs(y(3))*(y(6)^(2)+(sin(y(5)))^(2)*y(8)^(2));
    dxds_5 = y(6);
    dxds_6 = -(2/abs(y(3)))*y(4)*y(6)-(4/(3*y(1)))*y(2)*y(6)+((sin(2*y(5)))*(y(8)^(2))/2);
    dxds_7 = y(8);
    dxds_8 = -2*y(8)*((2/(3*y(1)))*y(2)+(cot(y(5)))*y(6)+(1/abs(y(3)))*y(4));

    dxds=[dxds_1; dxds_2; dxds_3; dxds_4; dxds_5; dxds_6; dxds_7; dxds_8];

   end
end
于 2016-02-18T09:49:40.633 回答