how to preallocate the variable in matlab code? - matlab

Question

while implementing kernel based grapg cut method, I am getting error at line: area(1+1)=999999999;
suggestion for correcting the error is line 147: the variable 'area' appears to change size on every loop iteration(within a script).
Considering preallocation for speed, please suggest me how to preallocate the variable area,in the matlab code?
Code:
clear all; close all;
%%%%%%%%%%%%%%%%%%%%%%%Main inputs and parameters%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%Note: The RBF-kernel parameters are given in function kernel RBF.m%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%Example with a color image%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%path = 'Images\Color_image.jpg';
%im = im2double(imread(path));
%alpha=1; %The weight of the smoothness constraint
%k =8; %The number of regions
%%%%%%%Example with a SAR image corrupted with a multiplicative noise%%%%%%
%%%%%%%%%%%%%%%%Uncomment the following to run the example)%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
path = 'Images\Sar_image.tif';
im = im2double(imread(path));
alpha=0.6;
k =4;
%%%%%%%%%%%%%%%%%%%%%%%%%%Example with a brain image%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%Uncomment the following to run the example)%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%path = 'Images\Brain_image.tif';
%im = im2double(imread(path));
%alpha=0.1;
%k =4;
sz = size(im);
Hc=ones(sz(1:2));
Vc=Hc;
i_ground = 0; % rank of the bakground for plotting, 0: the darkest;
%k-1 the brightest; 99: nowhere
diff=10000;
an_energy=999999999;
iter=0;
iter_v=0;
energy_global_min=99999999;
distance = 'sqEuclidean'; % Feature space distance
% Initialization: cluster the data into k regions
tic,
disp('Start kmeans');
data = ToVector(im);
[idx c] = kmeans(data, k, 'distance', distance,'EmptyAction','drop','maxiter',100);
c=c(isfinite(c(:,1)),:);
k=size(c,1);
k_max=k;
kmean_time=toc;
Dc = zeros([sz(1:2) k],'single');
c;
tic
while iter < 5
iter=iter+1;
clear Dc
clear K
c;
for ci=1:k
K=kernel_RBF(im,c(ci,:));
Dc(:,:,ci)=1-K;
end
clear Sc
clear K
%% The smoothness term
Sc = alpha*(ones(k) - eye(k));
gch = GraphCut('open', Dc, Sc, Vc, Hc);
[gch L] = GraphCut('swap',gch);
[gch se de] = GraphCut('energy', gch);
nv_energy=se+de;
gch = GraphCut('close', gch);
if (nv_energy<=energy_global_min)
diff=abs(energy_global_min-nv_energy)/energy_global_min;
energy_global_min=nv_energy;
L_global_min=L;
k_max=k;
nv_energy;
iter_v=0;
% Calculate region Pl of label l
if size(im, 3)==3 % Color image
for l=0:k-1
Pl=find(L==l);
card=length(Pl);
K1=kernel_RBF(im(Pl),c(l+1,1));K2=kernel_RBF(im(Pl),c(l+1,2));K3=kernel_RBF(im(Pl),c(l+1,3));
smKI(1)=sum(im(Pl).*K1); smKI(2)=sum(im(Pl+prod(sz(1:2))).*K2); smKI(3)=sum(im(Pl+2*prod(sz(1:2))).*K3);
smK1=sum(K1);smK2=sum(K2);smK3=sum(K3);
if (card~=0)
c(l+1,1)=smKI(1)/smK1;c(l+1,2)=smKI(2)/smK2;c(l+1,3)=smKI(3)/smK3;
else
c(l+1,1)=999999999;c(l+1,2)=999999999;c(l+1,3)=999999999;
end
end
end
if size(im, 1)==1 % Gray-level image
for l=0:k-1
Pl=find(L==l);
card=length(Pl);
K=kernel_RBF(im(Pl),c(l+1,1));
smKI=sum(im(Pl).*K);
smK=sum(K);
if (card~=0)
c(l+1,1)=smKI/smK;
else
c(l+1,1)=999999999;
end
end
end
c=c(c(:,1)~=999999999,:);
c_global_min=c;
k_global=length(c(:,1));
k=k_global;
else
iter_v=iter_v+1;
%---------------------------------
% Begin updating labels
%---------------------------------
% Calculate region Pl of label l
if size(im, 3)==3 % Color image
for l=0:k-1
Pl=find(L==l);
card=length(Pl);
K1=kernel_RBF(im(Pl),c(l+1,1));K2=kernel_RBF(im(Pl),c(l+1,2));K3=kernel_RBF(im(Pl),c(l+1,3));
smKI(1)=sum(im(Pl).*K1); smKI(2)=sum(im(Pl+prod(sz(1:2))).*K2); smKI(3)=sum(im(Pl+2*prod(sz(1:2))).*K3);
smK1=sum(K1);smK2=sum(K2);smK3=sum(K3);
% Calculate contour Cl of region Pl
if (card~=0)
c(l+1,1)=smKI(1)/smK1;c(l+1,2)=smKI(2)/smK2;c(l+1,3)=smKI(3)/smK3;
else
c(l+1,1)=999999999;c(l+1,2)=999999999;c(l+1,3)=999999999;
area(l+1)=999999999;
end
end
end
if size(im, 3)== 1 % Gray-level image
for l=0:k-1
Pl=find(L==l);
card=length(Pl);
K=kernel_RBF(im(Pl),c(l+1,1));
smKI=sum(im(Pl).*K);
smK=sum(K);
% Calculate contour Cl of region Pl
if (card~=0)
c(l+1,1)=smKI/smK;
else
c(l+1,1)=999999999;
area(l+1)=999999999;
end
end
end
c=c(c(:,1)~=999999999,:);
k=length(c(:,1));
end
end
L=L_global_min;
energy_global_min;
c=c_global_min;
size(c,1)
iter;
%Show the results
if size(im, 3)==3 % Color image
img=zeros(sz(1),sz(2),3);
j=1;
imagesc(im); axis off; hold on;
for i=0:k_max-1
LL=(L_global_min==i);
is_zero=sum(sum(LL));
if is_zero
img(:,:,1)=img(:,:,1)+LL*c(j,1);
img(:,:,2)=img(:,:,2)+LL*c(j,2);
img(:,:,3)=img(:,:,3)+LL*c(j,3);
j=j+1;
end
if i~=i_ground
color=[rand rand rand];
contour(LL,[1 1],'LineWidth',2.5,'Color',color); hold on;
end
end
figure(2);
imagesc(img); axis off;
end
if size(im, 3)==1 % Gray-level image
img=zeros(sz(1),sz(2));
j=1;
imagesc(im); axis off; hold on; colormap gray;
for i=0:k_max-1
LL=(L_global_min==i);
is_zero=sum(sum(LL));
if is_zero
img(:,:,1)=img(:,:,1)+LL*c(j,1);
j=j+1;
end
if i~=i_ground
color=[rand rand rand];
contour(LL,[1 1],'LineWidth',2.5,'Color',color); hold on;
end
end
figure(2);
imagesc(img); axis off;
end

Answer 1

A possible solution is to set the variable initially to zeros(k_max, 1 ).