Assignment has more non-singleton rhs dimensions than non-singleton subscripts

clc
clear
%Experimental data

xdata=[30  30  30 ;...
       60  60  60 ;...
       90  90  90 ;...
       120 120 120;...
       150 150 150;...
       180 180 180];
ydata=[0.031 0.033 0.029;...
       0.053 0.053 0.052;...
       0.066 0.071 0.065;...
       0.078 0.077 0.077;...
       0.085 0.083 0.087;...
       0.089 0.091 0.088];

k=0.01;
%The empty vector [] is a signal to Matlab to use the default options
options=[];

K=fminsearch(@SumErrorSquared, k, options, xdata, ydata);

%plot the results
clf
plot(xdata,ydata, '.r')
hold on
plot(xdata, (0.2/2)*(1-exp(-2*K*50*xdata/200)))

my function file

function r2 = SumErrorSquared(k,xdata,ydata)
k=k(1);
yfit =(0.2/2)*(1-exp(-2*k*50*xdata/200));
r = yfit - ydata; %residuals

%pause MATLAB for 0.1 seconds to give time to display plot
clf
plot(xdata,ydata, '.r')
hold on
plot(xdata, yfit)
pause(0.1)
r2 = sum(r.^2);

and I get this

Assignment has more non-singleton rhs dimensions than non-singleton subscripts

Error in fminsearch (line 200)
fv(:,1) = funfcn(x,varargin{:});

Error in bestfitline (line 11)
K=fminsearch(@SumErrorSquared, k, options, xdata, ydata);

can you help me please