Using for loops to generate an array?

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Dominic Lira
Dominic Lira 2015-11-6
回答： Matt Tearle 2015-11-6
I need to generate the array A = 1 2 3 4 5; 2 4 6 8 10; 3 6 9 12 15; 4 8 12 16 20; 5 10 15 20 25; using for loops. Don't have much experience with looping, and currently trying to understand it until it clicks. Help!

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TastyPastry
TastyPastry 2015-11-6
m = 7; n = 6;
A = zeros(m,n);
for i=1:m
A(i,:) = i:i:i*n;
end
This should work for any size array with rows m and columns n.
  2 个评论
Dominic Lira
Dominic Lira 2015-11-6
could you explain what's going on for the right side of the equation in line 4? (i:i:i*n)?
TastyPastry
TastyPastry 2015-11-6
In this notation, a:b:c, a is the starting value for a vector. b is the increment between each value. c is the maximum value of the vector. c may or may not appear as the last value in the vector.
If you look at the pattern you're generating, the first number of each line is also the line number you're currently writing. Therefore, the first value is i, the line you're currently writing. Now the increment in each line is also the line number you're generating (line 1's increment is 1, line 2's increment is 2, and so on), so the step is also i. Finally, i*n is the final value of your line, equal to the first value multiplied by the number of values in each line, since your increment is equal to the first value in each line.

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Matt Tearle
Matt Tearle 2015-11-6
TastyPastry's answer is perfectly correct, but it's worth asking an important clarification: why do you want to do it with a for-loop? This can be done far more neatly in MATLAB without any loops.

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