what I write to a file is different to what I read back from the same file

I calculate calibration constants using a simple program as shown below for two variables. The input data is coded into a table.

% Set up calibration of EXP from Table
close all;
clear all
format SHORTE
clc
ExpNumber=input('Enter Experiment Number = ')
CAL_Path='c:\UNSW\RESEARCH_ACTIVE\BP_Research\BP_UP_DOWN_INVASIVE_NEW\Data_CAL\'; 
CAL_File=[CAL_Path 'CAL_EXP_' num2str(ExpNumber) '.mat']

%==========================================================================
% Enter Calibration Data into matrix below
Pressure=[0 44.2 91 139.2 186 242.4]
Count_cp=[168 12002 24002 36005 48008 62008];
Count_iabp=[2206 12124 22825 33549 44318 57075];
Calibration=table(Pressure, Count_cp, Count_iabp)

disp(ExpNumber)
disp([Calibration.Pressure' Calibration.Count_cp' Calibration.Count_iabp'])
%==========================================================================

% First for CP
x=Calibration.Count_cp';
y=Calibration.Pressure';
[f,q] = fit(x,y,'poly1')
figure(10)
plot(f,x,y)

% Now for IABP
X=Calibration.Count_iabp';
[F,Q]=fit(X,y,'poly1')
figure(20)
plot(F,X,y)
cp_cal=[f.p1 f.p2];
iabp_cal=[F.p1 F.p2];
save(CAL_File, 'ExpNumber','Calibration','cp_cal','f','q','iabp_cal','F','Q') 
clear ExpNumber Calibration cp_cal f q iabp_cal F Q                    % Should not be necessary as I clear all variable on start of program
disp('Ended normally ***********')

This produces a file CAL_EXP_10, as the ExpNumber entered is 10

I then wrote a simple program to check the data written by reading it back, using the simple program, ReadCalFile.m

% Read CAL file
clear all
clc
Exp=input('Enter Experiment Number = ')        % Required calibration data to read 
CAL_Path='c:\UNSW\RESEARCH_ACTIVE\BP_Research\BP_UP_DOWN_INVASIVE_NEW\Data_CAL\'; 
CAL_File=[CAL_Path 'CAL_EXP_' num2str(Exp) '.mat']
load CAL_File
who
disp(Exp)
disp(ExpNumber)
disp([Calibration.Pressure' Calibration.Count_cp' Calibration.Count_iabp'])
%---------------------------------------------------------------------------------------------------------end of read program

The data read back when Exp is selcted as 10 returns data fro CAL_EXP_12.mat as shown below,

Enter Experiment Number = 10

Exp =

10            % Number of requested cal file to read


CAL_File =

'c:\UNSW\RESEARCH_ACTIVE\BP_Research\BP_UP_DOWN_INVASIVE_NEW\Data_CAL\CAL_EXP_10.mat'


Your variables are:

CAL_File     Calibration  ExpNumber    Q            f            q            
CAL_Path     Exp          F            cp_cal       iabp_cal     

10            % Correct file requested

12            % Incorrect ExpNumber returned

0           1.6700e+02   6.2500e+02            % Data matrix returned does not match data for EXP_10
4.3200e+01   1.2006e+04   1.0620e+04
9.1700e+01   2.4010e+04   2.1303e+04
1.4000e+02   3.6015e+04   3.2152e+04
1.8710e+02   4.8009e+04   4.3059e+04
2.4160e+02   6.2001e+04   5.5854e+04

Answer 1

[Stephen23]

Because you are reading a different file than you are writing. The main problem is this line here

load CAL_File

where you LOAD a file literally named "CAL_File" using command syntax (you should have used function syntax):

https://www.mathworks.com/help/matlab/matlab_prog/command-vs-function-syntax.html

After fixing that and some other "features" of your code and testing it here:

ExpNumber = 10;
CAL_Path  = '.'; 
CAL_File  = fullfile(CAL_Path,['CAL_EXP_',num2str(ExpNumber),'.mat']);
% Enter Calibration Data into matrix below
Pressure   = [  0; 44.2;   91; 139.2;  186;242.4];
Count_cp   = [168;12002;24002; 36005;48008;62008];
Count_iabp = [2206;12124;22825;33549;44318;57075];
% First for CP
[f,q] = fit(Count_cp,Pressure,'poly1');
% Now for IABP
[F,Q] = fit(Count_iabp,Pressure,'poly1');
cp_cal   = [f.p1,f.p2];
iabp_cal = [F.p1,F.p2];
save(CAL_File, 'ExpNumber','cp_cal','f','q','iabp_cal','F','Q') 

clear all

ExpNum   = 10;
CAL_Path = '.'; 
CAL_File = fullfile(CAL_Path,['CAL_EXP_',num2str(ExpNum),'.mat']);
load(CAL_File)
who

Your variables are:

CAL_File   CAL_Path   ExpNum     ExpNumber  F          Q          cp_cal     f          iabp_cal   q          

disp(ExpNum)

    10

disp(ExpNumber)

    10

Tips:

• avoid using variable/function names that only differ by case. These cause plenty of confusion.
• use FULLFILE rather than concatenating text together.
• if you require column vectors then create column vectors.
• More here: https://www.mathworks.com/matlabcentral/discussions/tips/847916-experts-of-matlab-how-did-you-learn-any-advice-for-beginner-intermediate-users

[Branko Celler]

Thank you! This was a subtlety that escaped me and caused me a lot of time wasting. I will read the advisory URLs you have sent me!