MATLAB: Nested FOR loops and creating text file (3d-layers) too slow.

MATLABnested for loopprogrammingslow

Hello everyone,
I am pretty new with Matlab. I am facing a problem concering nested for-loops and creating a text file. It is too slow. The text file contains data for 3d-layers.
If the number of layers and rows and columns in each layer are too big, it takes lots of hours to execute the code.
If anyone here can help me regarding to optimize my code or telling me an alternate to solve this problem, it would be very helpful.
Thank you very much.
clc
clear all
b=100;
l=150;
d=0.1;
dn=1.0;
nnR=b/dn+1;
nnC=l/dn+1;
nL=d/0.1+1;
R=1;
C=1;
L=0;
x=0;
y=0;
z=0;
space='          ';
add=0;
nline=sprintf('Start\ntextfileindex\n$    nod               row               column               layer                        \n');
% fileID=fopen('node.txt','w');
% fprintf(fileID,'%s', q);
for b = 1:nL
  
for i = 1:nnR
    dummieR=R
    for i = 1:nnC
        abc=b;
        abc=num2str(abc);
        if b<10
            
        abc=strcat('0',abc)
        else
            abc=b;
        end
        dummieC=C
        numC=num2str(dummieC)
        dummiex=x
        dummiey=y
        dummiez=z
    numz = sprintf('%.4f',dummiez)   
    numx = sprintf('%.4f',dummiex)
    numy = sprintf('%.4f',dummiey)
    
%     numx = sprintf('%.4f',dummiex)

    if C<100 && C>9
        numC=strcat('0',numC)
    end
    if C<10
        numC=strcat('00',numC)
    end
        
        numR=num2str(dummieR)
    if R<100 && R>9
        numR=strcat('0',numR)
    end
    if R<10
        numR=strcat('00',numR)
    end
%     dummiex=x
%     numx = sprintf('%.4f',dummiex)
%     numx=num2str(dummiex)
   if dummiex<100 && dummiex>9.9999
    def= "\n"+abc+numR+numC+"         "+numx
   elseif dummiex<10
     def= "\n"+abc+numR+numC+"          "+numx
   else
      def= "\n"+abc+numR+numC+"        "+numx
   end
   if dummiey<100 && dummiey>9.9999
    def= def+"         "+numy
   elseif dummiey<10
     def= def+"          "+numy
   else
      def= def+"        "+numy
   end
     
 if nL<10
 def= def+"           "+numz
 else
  def= def+"          "+numz 
 end
    C=C+1;
    nline= strcat(nline,def)
    nline= sprintf(nline)
    x=x+dn;
    end
    R=R+1;
    C=1;
    y=y+dn;
    x=0;
end
z=z+0.1;
x=0;
y=0;
C=1;
R=1;
end
nline=sprintf(nline+ "\n" + "END")
fileID=fopen('textfilem.txt','wt');
fprintf(fileID, nline);

Best Answer

So, as suspected, just generate the data to print and use the desired formatting string:
% generate some sample data...
A=1001000+[1:11];
B=0:5:50;
C=[A.' B.' zeros(numel(A),2)];
% define the desired format for output file...
fmt=['%08d' repmat('%12.4f',1,3) '\n'];
% Illustrate what will get to command line...
>> fprintf(1,fmt,C.')
01001001      0.0000      0.0000      0.0000
01001002      5.0000      0.0000      0.0000
01001003     10.0000      0.0000      0.0000
01001004     15.0000      0.0000      0.0000
01001005     20.0000      0.0000      0.0000
01001006     25.0000      0.0000      0.0000
01001007     30.0000      0.0000      0.0000
01001008     35.0000      0.0000      0.0000
01001009     40.0000      0.0000      0.0000
01001010     45.0000      0.0000      0.0000
01001011     50.0000      0.0000      0.0000
>>
NB1: Internal Matlab storage order is column major so must transpose C to output by row for sequential file.
NB2: The first column is possible to be written as part of formatting statement as well if the values are just 1:N. Include the literal string '0100' in the format string as '0100%05d' to handle i from 1:99999
Related Question