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#### MATLAB tutors help, Plot the number of bacteria (**N**) as a function of time (**t**) and find the time after which all of the bacteria have died

% plot no of bacteria instead of rate of change /* dsp projects matlab with code*/

% 6th oct 09

clc;

clear;

[data x y] = readplot(‘experimental_dNdt.txt’,6,2);

noofbacteria = zeros(length(y),1);

for i = 1:length(y)

noofbacteria(i) = sum(y(1:i)) ;

end /*help in matlab project coding*/

plot(x,noofbacteria);

xlabel(‘Time’);

ylabel(‘No. of Bacteria’);

% Use newton raphson to find the zero of the no of bacteria

p = polyfit(x,noofbacteria,3);

r = newtonraph(p);

disp(‘The point at which the no of bacteria become zero’);

disp(real(r(2)));

### Detail discussion given below for the Matlab Code

function [labels,x,y] = readndplot(fname,ncols,nhead,nlrows)

*readColData reads data from a file containing data in columns

* that have text titles and possibly other header text

* Synopsis: /* MATLAB TUTOR SERVICE*/

* [labels,x,y] = readColData(fname)

* [labels,x,y] = readColData(fname,ncols)

* [labels,x,y] = readColData(fname,ncols,nhead)

* [labels,x,y] = readColData(fname,ncols,nhead,nlrows)

* Input:

* fname = name of the file containing the data (required)

* ncols = number of columns in the data file. Default = 2. A value

* of ncols is required only if nlrows is also specified.

* nhead = number of lines of header information at the very top of

* the file. Header text is read and discarded. Default = 0.

* A value of nhead is required only if nlrows is also specified.

* nlrows = number of rows of labels. Default = 1

* Output:

* labels = matrix of labels. Each row of lables is a different

* label from the columns of data. The number of columns

* in the labels matrix equals the length of the longest

* column heading in the data file. More than one row of

* labels is allowed. In this case the second row of column

* headings begins in row ncol+1 of labels. The third row

* column headings begins in row 2*ncol+1 of labels, etc.

* NOTE: Individual column headings must not contain blanks

* x = column vector of x values

* y = matrix of y values. y has length(x) rows and ncols columns

* Author:

* Gerald Recktenwald, gerry@me.pdx.edu

* Portland State University, Mechanical Engineering Department

* 24 August 1995

* process optional arguments

if nargin < 4

nlrows = 1; % default

if nargin < 3

nhead = 0; % default

if nargin < 2

ncols = 2; % default

end

end

end

* open file for input, include error handling

fin = fopen(fname,’r’);

if fin < 0

error([‘Could not open ‘,fname,’ for input’]);

end

* Preliminary reading of titles to determine number of columns

* needed in the labels matrix. This allows for an arbitrary number

* of column titles with unequal (string) lengths. We cannot simply

* append to the labels matrix as new labels are read because the first

* label might not be the longest. The number of columns in the labels

* matrix (= maxlen) needs to be set properly from the start.

* Read and discard header text on line at a time

for i=1:nhead, buffer = fgetl(fin); end

maxlen = 0;

for i=1:nlrows

buffer = fgetl(fin); % get next line as a string

for j=1:ncols

[next,buffer] = strtok(buffer); parse next column label

maxlen = max(maxlen,length(next)); % find the longest so far

end

end

* Set the number of columns in the labels matrix equal to the length

* of the longest column title. A complete preallocation (including

* rows) of the label matrix is not possible since there is no string

* equivalent of the ones() or zeros() command. The blank() command

* only creates a string row vector not a matrix.

labels = blanks(maxlen);

frewind(fin); % rewind in preparation for actual reading of labels and data

* Read and discard header text on line at a time

for i=1:nhead, buffer = fgetl(fin); end

* Read titles for keeps this time

for i=1:nlrows

buffer = fgetl(fin); % get next line as a string

for j=1:ncols

[next,buffer] = strtok(buffer); % parse next column label

n = j + (i-1)*ncols; pointer into the label array for next label

labels(n,1:length(next)) = next; % append to the labels matrix

end

end

* Read in the x-y data. Use the vetorized fscanf function to load all

* numerical values into one vector. Then reshape this vector into a

* matrix before copying it into the x and y matrices for return.

data = fscanf(fin,’%f’); * Load the numerical values into one long vector

nd = length(data); total number of data points

nr = nd/ncols; number of rows; check (next statement) to make sure

if nr ~= round(nd/ncols)

fprintf(1,’\ndata: nrow = %f\tncol = %d\n’,nr,ncols);

fprintf(1,’number of data points = %d does not equal nrow*ncol\n’,nd);

error(‘data is not rectangular’)

end

data = reshape(data,ncols,nr)’; % notice the transpose operator

x = data(:,1);

y = data(:,2:ncols);

% end of readColData.m