How can I write these functions to the press

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Bilal Ates
Bilal Ates 2020-6-26
回答： Ameer Hamza 2020-6-26
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Bilal Ates
Bilal Ates 2020-6-26
Sorry I typed it wrong. I want to write in matlab
Bilal Ates
Bilal Ates 2020-6-26
clc; % Clears the screen
clear all;
h=0.25; % step size
x = 0:h:1; % Calculates upto y(4)
y = zeros(1,length(x));
z = ???
y(0) = 2; % initial condition
z(0) = 4;
F_xy = ?????????? % change the function as you desire
F_xz = ??????????
for i=1:(length(x)-1) % calculation loop
k_1 = F_xy(x(i),y(i));
k_2 = F_xy(x(i)+0.5*h,y(i)+0.5*h*k_1);
k_3 = F_xy((x(i)+0.5*h),(y(i)+0.5*h*k_2));
k_4 = F_xy((x(i)+h),(y(i)+k_3*h));
y(i+1) = y(i) + (1/6)*(k_1+2*k_2+2*k_3+k_4)*h; % main equation
end

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回答（1 个）

Ameer Hamza
Ameer Hamza 2020-6-26
You can use ode45() to solve such a system of ODEs.
ic = [2; 4];
xspan = [0 1];
[x, Q] = ode45(@odeFun, xspan, ic);
y_sol = Q(:,1);
z_sol = Q(:,2);
plot(x, Q);
legend({'y', 'z'}, 'FontSize', 16);
function dQdx = odeFun(x, Q)
% Q(1) <=> y, Q(2) <=> z
y = Q(1);
z = Q(2);
dydx = -2*y + 4*exp(-x) + exp(-1000*z^2);
dzdx = -y*z^2/3;
dQdx = [dydx; dzdx];
end

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