dividing defined variable by named variable

Question

Liam Bates 2022-9-28

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评论： Image Analyst 2022-9-28

everytime i try to divide a defined variable by a calculated variable, it only outputs one number multiple times. What syntax am i missing?

d=1:.2:3;

a=sqrt((d.^2)*(3^2));

Y=d./a

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Stephen23 2022-9-28

编辑：Stephen23 2022-9-28

" it only outputs one number multiple times."

Because that is the correct result for your code, which is equivalent to d./(3*d)

"What syntax am i missing?"

Because you did not state the expected output nor what you are trying to achieve, we cannot guess the syntax that is required to achieve an unstated goal.

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Answer 1

Image Analyst 2022-9-28

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Well yeah. Just look at the numbers:

d = 1 : 0.2 : 3
d = 1×11
    1.0000    1.2000    1.4000    1.6000    1.8000    2.0000    2.2000    2.4000    2.6000    2.8000    3.0000
a = sqrt((d.^2)*(3^2))
a = 1×11
    3.0000    3.6000    4.2000    4.8000    5.4000    6.0000    6.6000    7.2000    7.8000    8.4000    9.0000
Y = d ./ a
Y = 1×11
    0.3333    0.3333    0.3333    0.3333    0.3333    0.3333    0.3333    0.3333    0.3333    0.3333    0.3333

They all look right to me. Exactly what output numbers did you expect? Tell me which element of Y it got wrong and should be a different number.

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Liam Bates 2022-9-28

is it just how the matrix is set up? would i need a loop instead?

Image Analyst 2022-9-28

You can define "a" differently then, like perhaps add noise

d = 1 : 0.2 : 3
d = 1×11
    1.0000    1.2000    1.4000    1.6000    1.8000    2.0000    2.2000    2.4000    2.6000    2.8000    3.0000
a = sqrt((d.^2)*(3^2)) + rand(size(d))
a = 1×11
    3.3071    4.0240    4.6150    5.2096    5.6304    6.3306    7.5081    8.0647    7.8299    8.5545    9.7844
Y = d ./ a
Y = 1×11
    0.3024    0.2982    0.3034    0.3071    0.3197    0.3159    0.2930    0.2976    0.3321    0.3273    0.3066

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Answer 2

Walter Roberson 2022-9-28

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a=sqrt((d.^2)*(3^2))

3^2 is 9 so inside the sqrt() you have 9*d^2. sqrt() of that is sqrt(9)*sqrt(d^2). For positive d that is 3*d

Y = d ./ a

So you have d divided by 3*d. For non-zero d that is going to be 1/3 no matter what the positive value of d is. For negative d you would get -1/3. For 0 you get nan.