Why does a for loop 1:1:n index at a different rate than +1?

Hello, I am reading the first couple values from a data file, but I noticed that values in my for loop were not matching the values in the stored in my data file. Speficially the second loop which displays both the value of i and the of Z.

My questions are:

1: Why does the second for loop behaive differently than the first; shouldn't i always increment by whole number values?

2. Why does the second for loop contain more than 5 iterations?

3. Why are the values of Z in the second for loop different than what is actually store in them? The values from Z at the end give the correct values from the Data csv file.

Thank you for any information you can provide.

The code:

% Goal: Read data from Shipmotion CSV file
clc;

Data = csvread('RegularShipMotion_Hs2_Tp15_Vs15_HG0.csv', 1, 0, 'A37..G65037');
%number of data points (rows) from datafile
n = 5;

%Column A: Time
%Column D: Z
% Time (t)
t = Data(2:n,[2]);
X = Data(2:n,[3]);          %Nonzero for RegularShip...
Y = Data(2:n,[4]);
Z = Data(2:n,[5]);          %Nonzero for RegularShip...
Pitch = Data(2:n,[6]);      
Roll = Data(2:n,[7]);       %Nonzero for RegularShip...
Yaw = Data(2:n,[8]); 

%Loop testing
fprintf("\nRunning...")
for i=1:1:n
    fprintf("the value of i is %f \n", i)
end

fprintf("\n")

for i=1:1:n
    fprintf("the value of i is %f and the value of z is %f \n", i, Z)
end

fprintf("\n")

Z

[Cameron Eggart]

My output is this:

the value of i is 1.000000

the value of i is 2.000000

the value of i is 3.000000

the value of i is 4.000000

the value of i is 5.000000

the value of i is 1.000000 and the value of z is 3.015000

the value of i is 3.005000 and the value of z is 2.995000

the value of i is 2.982000 and the value of z is the value of i is 2.000000 and the value of z is 3.015000

the value of i is 3.005000 and the value of z is 2.995000

the value of i is 2.982000 and the value of z is the value of i is 3.000000 and the value of z is 3.015000

the value of i is 3.005000 and the value of z is 2.995000

the value of i is 2.982000 and the value of z is the value of i is 4.000000 and the value of z is 3.015000

the value of i is 3.005000 and the value of z is 2.995000

the value of i is 2.982000 and the value of z is the value of i is 5.000000 and the value of z is 3.015000

the value of i is 3.005000 and the value of z is 2.995000

the value of i is 2.982000 and the value of z is

Z =

3.0150

3.0050

2.9950

2.9820

>>

Answer 1

[Voss]

Look what happens when you pass a non-scalar array to fprintf():

Z = [1; 2; 3];
fprintf('the value of Z is: %f',Z);

the value of Z is: 1.000000the value of Z is: 2.000000the value of Z is: 3.000000

The entire format string is repeated for each element. That's what's going on here, since you are sending the whole array Z to fprintf() each time. If you want to see the ith element of Z each time, you can say:

for i=1:1:n
    fprintf("the value of i is %f and the value of z is %f \n", i, Z(i))
end

[Cameron Eggart]

This is clear and address my question. Thank you for your time!

[Voss]

You're welcome! Glad I could help