two variables with known values in equations; use loop in matlab

Question

Norzuria Ibrahim 2015-9-29

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评论： Norzuria Ibrahim 2015-9-29

Hi I have question to ask. I have 3 variables with known variables, x, y, z.

x= 3, 1 , 4, 2, 1
y=3,4 ,5,1,1
z=2,2,1,2,2

I need to apply those variables in two related equations

d=x+y+2z
e=2d+xyz

how to solve this using loop

what I did

x=[3 1 4 2 1];
y=[3 4 5 1 1];
z=[2 2 1 2 2];
for i=1:length(x);
   j=1:length(y);
   k=1:length(z);
   d=x(i)+y(j)+2*z(k)
   d=d+1
   e=2*d+(x(i)*y(j)*z(k))
end

did not work

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Answer 1

Andrei Bobrov 2015-9-29

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在 MATLAB Online 中打开

x=[3 1 4 2 1];
y=[3 4 5 1 1];
z=[2 2 1 2 2];
d=x+y+2*z;
e=2*d+x.*y.*z;

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Walter Roberson 2015-9-29

The code that Andrei provided does all of them at the same time. No loop is required.

Norzuria Ibrahim 2015-9-29

sorry.my mistake..you already told me how to wrote it above.anyway,thanks guys for your superb answers.

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Answer 2

WAT 2015-9-29

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编辑：WAT 2015-9-29

在 MATLAB Online 中打开

It's a little unclear from your question, but if you mean you have 3 dependent variables (x,y,z) each observed at 5 different values of some independent variable (for example, x(t),y(t) and z(t)), and you want the values of c and e at those same times, then all you need to do is

 d=x+y+2*z 
 e=2*d+x.*y.*z

The decimal in front of the multiply tells MATLAB to do the multiplication componentwise, rather than matrix multiplication.

Unless you're required to use a loop (for a HW assignment), in which case it would be something like

 d = zeros(1,5);
 e = zeros(1,5);
 for i = 1:5
   d(i) = x(i) + y(i) + 2*z(i);
   e(i) = 2*d(i) + x(i)*y(i)*z(i);
 end

But you don't want to do it this way unless you're explicitly required to use a loop.

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Norzuria Ibrahim 2015-9-29

编辑：Norzuria Ibrahim 2015-9-29

I think the code you wrote is right. But, the variables x, y and z have values like I wrote above. How to write the data of the variables in matlab and use loop?

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