Second Order Difference in MATLAB

m = magic(4)
Dd = diff(diag(m),2) %diagonal
Dm = diff(diag(rot90(m)),2) %minor diagonal

Unwrap the phase

clear all
clc
s = size(phase);
count = s(1);
for i=1:count-1

if(phase(i+1)<phase(i))
phase(i+1:end)=phase(i+1:end) + 6.28;
end
end

Importance of trim in string concatenation in Fortran 90

It is very important while concatenating strings as not doing it may lead to issues with the size of string array.

Fortran Integer to String and vice versa

Integer I
Character* str
I = 9999
Write( str, '(i10)' ) I
End
Here it will be i4 if there are 4 words, or as suitable

Integer I
Character* str
I = 9999
read( str, '(i10)' ) I
End

Read mixed csv file in MATLAB

Use this function

function lineArray = read_mixed_csv(fileName,delimiter)
fid = fopen(fileName,'r');   %# Open the file
lineArray = cell(100,1);     %# Preallocate a cell array (ideally slightly
%#   larger than is needed)
lineIndex = 1;               %# Index of cell to place the next line in
nextLine = fgetl(fid);       %# Read the first line from the file
while ~isequal(nextLine,-1)         %# Loop while not at the end of the file
lineArray{lineIndex} = nextLine;  %# Add the line to the cell array
lineIndex = lineIndex+1;          %# Increment the line index
nextLine = fgetl(fid);            %# Read the next line from the file
end
fclose(fid);                 %# Close the file
lineArray = lineArray(1:lineIndex-1);  %# Remove empty cells, if needed
for iLine = 1:lineIndex-1              %# Loop over lines
lineData = textscan(lineArray{iLine},'%s',...  %# Read strings
'Delimiter',delimiter);
lineData = lineData{1};              %# Remove cell encapsulation
if strcmp(lineArray{iLine}(end),delimiter)  %# Account for when the line
lineData{end+1} = '';                     %#   ends with a delimiter
end
lineArray(iLine,1:numel(lineData)) = lineData;  %# Overwrite line data
end
end

And then use it as

source : http://stackoverflow.com/questions/4747834/import-csv-file-with-mixed-data-types

Then after that we get a cell in data variable, to make a matrix of this cell use

data_m = str2double(data);

Non Linear Dynamics and Chaos – Steven H Strogatz (Notes)                         Stream Function and Velocity Potential       courtsey : http://nptel.ac.in/courses/101103004/12