Why does the line plot depend on the generator type in a for loop ?

I have :

• a set of points in two dimensions given by their coordinates x_stations and y_stations;
• a set of couples of points given by the indices of point 1 (couples_st1) and point 2 (couples_st2) for each couple;
• a subset i_subset of those couples

I would like to plot i_subset graphically as lines linking point 1 and point 2 for each couple in the subset.

The problem : depending how I am looping on i_subset :

for i = i_subset

i_couple = i;

% some code...

% generate plot

% ouptut the plotted vectors

end

or

for i = 1:length(i_subset)

i_couple = i_subset(i);

% some code ...

% generate plot

% ouptut the plotted vectors

end

I get the same output of plotted vectors, but not the same plots. Why ?

A minimal example is enclosed with input data. Just run "main_minimal_example.m".

main_minimal_example

max difference in x outputs : 0
max difference in y outputs : 0

Thank you !

Answer 1

[Voss]

The i_subset passed in to make_line_plot.m is a column vector, and that is assigned to generator if mode == 1. Then generator is used in the for loop

for i_gen = generator

A for loop iterates over the columns of what you give it, so this loop iterates one time, with i_gen being generator.

When mode is 0, then generator is 1:length(i_subset), which is a row vector, and the for loop operates as intended (I assume).

To get the mode == 1 case to work like the mode == 0 case, one way would be to make the for loop iterate over elements of generator, as in:

for i_gen = generator(:).'

[ From the documentation for for, when you have for index = valArray:

valArray — Create a column vector, index, from subsequent columns of array valArray on each iteration. For example, on the first iteration, index = valArray(:,1). The loop executes a maximum of n times, where n is the number of columns of valArray ]

[Alexandre Kazantsev]

Great answer, i've just understood something basic. Thank you

[Voss]

You're welcome!