Error: File: slopfield.m Line: 1 Column: 30 Invalid expression. Check for missing multiplication operator, missing or unbalanced delimiters, or other syntax error. To construct matrices, use brackets instead of parentheses.

Hi i am working on this code:

function [t,y] = eulode(dxdt,[0,0.4],2,0.1,varargin)

% input:

if nargin<4,error('at least 4 input arguments required'),end

ti = tspan(1);tf = tspan(2);

if ~(tf>ti),error('upper limit must be greater than lower'),end

t = (ti:h:tf)'; n = length(t);

if t(n)<tf

t(n+1) = tf;

n = n+1;

end

y = y0*ones(n,1); %preallocate y to improve efficiency

for i = 1:n-1 %implement Euler's method

y(i+1) = y(i) + dydt(t(i),y(i),varargin{:})*(t(i+1)-t(i));

end

but i keep getting the error "Error: File: slopfield.m Line: 1 Column: 30 Invalid expression. Check for missing multiplication operator, missing or unbalanced delimiters, or other syntax error. To construct matrices, use brackets instead of parentheses.

[Peter O]

It sounds like slopfield is getting called and there's a syntax error in that file. Is that another function you've created? My hunch would be that the dydt.m function calls it.

Type

edit slopfield 

to open it, and see if the MLINT syntax checker highlights a line somewhere.

[Anonymous]

when i type edit slopfield it says "does not exist"

Answer 1

[Walter Roberson]

function [t,y] = eulode(dxdt,[0,0.4],2,0.1,varargin)

That is invalid syntax for a function definition. The part in () can only have a list of pure variable names or the special keyword varargin, and can never have constants or indexed variables.

Your code uses variable names tspan and h without defining them.