Building a matrix with a for-loop

2015 10 25
2 个回答
更新时间：2015 10 25
8 次查看（30 天）

0 个投票

Hello, I am constructing a matrix using the following program:
%Program HW13.m
x = 35;
y = 26;
n = 5;
for i = 1:1:n+1
x(i+1) = 18*x(i) - 11*y(i);
y(i+1) = 8*x(i) - y(i);
end
The for-loop generates two matrices, one for "x" and one for "y". However, I need to create new matrix: column 1 with the "i" values, column 2 with the iterated "x" values, column 3 with the iterated "y" values, and column 4 with "x/y" values. Any suggestions on how to do this?

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回答（2 个）

Walter Roberson
Walter Roberson 2015-10-25

1 个投票

[(1:n+1).', x(:), y(:), x(:)./y(:)]

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Viktoria Kolpacoff
Viktoria Kolpacoff 2015-10-25
Tried this command; however it says that the dimensions are not consistent.
Star Strider
Star Strider 2015-10-25
That should be:
[(1:n+2).', x(:), y(:), x(:)./y(:)]
because of the way the indices work, so the number of elements is n+1+1.

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Andrei Bobrov
Andrei Bobrov 2015-10-25

0 个投票

n = 5;
out = zeros(n+2,4);
out(1,2) = 35;
out(1,3) = 26;
for ii = 1:n+1
out(ii+1,2) = 18*out(ii,2) - 11*out(ii,3);
out(ii+1,3) = 8*out(ii,2) - out(ii,3);
end
out(:,1) = 1:n+2;
out(:,end) = out(:,2)./out(:,3);

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Viktoria Kolpacoff
Viktoria Kolpacoff 2015-10-25
编辑：Viktoria Kolpacoff 2015-10-25
Thank you for your help. However, when I run the program, I get:
out =
1.0e+07 *
0.0000 0.0000 0.0000 0.0000
0.0000 0.0000 0.0000 0.0000
0.0000 0.0003 0.0002 0.0000
0.0000 0.0034 0.0025 0.0000
0.0000 0.0335 0.0245 0.0000
0.0000 0.3334 0.2434 0.0000
0.0000 3.3235 2.4235 0.0000
Andrei Bobrov
Andrei Bobrov 2015-10-25 
>> format short g
>> out
out =
            1           35           26       1.3462
            2          344          254       1.3543
            3         3398         2498       1.3603
            4        33686        24686       1.3646
            5    3.348e+05    2.448e+05       1.3676
            6   3.3336e+06   2.4336e+06       1.3698
            7   3.3235e+07   2.4235e+07       1.3714
Stephen23
Stephen23 2015-10-25
编辑：Stephen23 2015-10-25
@Viktoria Kolpacoff: what is the problem with that output? Remember that the factor 1.0e+07 * applies to all elements of the displayed array. You can use format to change how output is displayed in the command window.

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