what is wrong with my code?

t=86400;
v=10.^-5;
D=10.^-7;
x=0:0.01:2;
%Calcuate the concentration in ( mol/l)
conc=(1./sqrt(4*pi*D*t)*exp.(-1*((x-v*t).^2./4*D)));

Answer 1

[Jan]

conc=(1./sqrt(4*pi*D*t)*exp.(-1*((x-v*t).^2./4*D)));
%                          ^ 

This is interpreted as "exp" beeing a struct and "(-1*((x-v*t).^2./4*D)))" is the dynamic fieldname.

Such typos are more obvious if you use spaces:

conc = 1 ./ sqrt(4 * pi * D * t) * exp(-D * (x - v * t) .^ 2 ./ 4);

The spaces avoid another ambiguity also:

a.^2./x
% Does this mean:
a .^ 2.0 / x
% or:
a .^ 2 ./ x

Although the Matlab's interpreters have strict and unique rules for these cases, a human reader can be confused.

Answer 2

[DGM]

Don't need a dot in exp()

conc=(1./sqrt(4*pi*D*t)*exp(-1*((x-v*t).^2./4*D)));

This is no comment on the correctness of any math, though.