# Error RungeKutta method......not enough input arguments

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Camilo Sánchez on 10 Nov 2017
Commented: Camilo Sánchez on 10 Nov 2017
function [xSol,ySol] = runKut4(dEqs,x,y,xStop,h)
%function [xSol,ySol] = runKut4(dEqs,x,y,xStop,h)
% 4th-order Runge--Kutta integration.
% USAGE: [xSol,ySol] = runKut4(dEqs,x,y,xStop,h)
% INPUT:
% dEqs = handle of function that specifies the 1st-order differential equations
% F(x,y) = [dy1/dx dy2/dx dy3/dx ...].
% x,y = initial values; y must be row vector.
% xStop = terminal value of x.
% h = increment of x used in integration.
% OUTPUT:
% xSol = x-values at which solution is computed.
% ySol = values of y corresponding to the x-values.
if size(y,1) > 1;
y = y';
end % y must be row vector
xSol = zeros(2,1);
ySol = zeros(2,length(y));
xSol(1)= x;
ySol(1,:)=y;
i = 1;
while x < xStop
i = i + 1;
h = min(h,xStop - x);
K1 = h*feval(dEqs,x,y);
K2 = h*feval(dEqs,x + h/2,y + K1/2);
K3 = h*feval(dEqs,x + h/2,y + K2/2);
K4 = h*feval(dEqs,x+h,y + K3);
y = y + (K1 + 2*K2 + 2*K3 + K4)/6;
x = x + h;
xSol(i) = x;
ySol(i,:) = y; % Store current soln.
end
-------------------------------------------------------------------------
function F = fex7_4(x,y)
% Differential. eqs. used in Example 7.4
F = zeros(1,2);
F(1) = y(2); F(2) = -0.1*y(2) - x;
[x,y] = runKut4(@fex7_4,0,[0 1],2,0.25);
printSol(x,y,1)
--------------------------------------------------------------
>> fex7_4 Error using fex7_4 (line 4) Not enough input arguments.
not enough input arguments ??????

James Tursa on 10 Nov 2017
Please show us exactly how you are calling your function (i.e., give us the inputs), and then copy & paste the entire error message for us to see.
Camilo Sánchez on 10 Nov 2017
Upss sorry....here is:
[x,y] = runKut4(@fex7_4,0,[0 1],2,0.25);
printSol(x,y,1)
Camilo Sánchez on 10 Nov 2017
>> fex7_4 Error using fex7_4 (line 5) Not enough input arguments.

Mischa Kim on 10 Nov 2017
Edited: Mischa Kim on 10 Nov 2017
Store runKut4 and fex7_4 in separate m-files and then execute
[x,y] = runKut4(@fex7_4,0,[0 1],2,0.25);
e.g. in the MATLAB command window and you should get results for x and y. printSol is probably another function you have access to, I do not know. But you could simply use plot to plot the solution trajectory.

#### 1 Comment

Camilo Sánchez on 10 Nov 2017
Thanks friend, I found the problem and the other function.