MATLAB: Can anyone help to creat this vector

homeworkmatrix arraymatrix manipulationvector

A vector is given by: V = [5; 17; 3; 8; 0; 1; 12; 15; 20; 6; 6; 4; 7; 16]. Write a program in the form of a script file, which doubles the positive elements that are divisible by 3 and / or by 5, and raises to the cube the negative elements greater than -5 ie: WI= 1/ 2*Vi if Vi>0 multiple of 3 and / or 5 2/ (Vi)^3 if Vi<0 greater than -5 3/ Vi otherwise

Best Answer

You're close, but you need to handle the W(i)=V(i) differently. The way you have it currently coded, this line is overwriting all of your other code. Maybe use some "elseif" clauses. Also you should probably use the scalar logical operators "&&" and "||" for this and parentheses to make the logical test exactly what you want. The parentheses are particularly important to use when you have multiple comparisons going on within one test to make sure the order they are evaluated in is exactly what you want. Getting in the habit of using the scalar logical operators "&&" and "||" instead of the element-wise operators "&" and "|" will become important when you forget at some point in the future to use subscripts. The "&&" and "||" will generate an error which will give you an immediate feedback that something is wrong with your code and exactly where it is wrong in your code. The "&" and "|" will often simply result in a wrong answer and then you have to track down where your code went wrong. E.g.,

    if V(i)> 0 && (mod(V(i),3)==0 || mod(V(i),5)==0)
        W(i) = V(i)*2;
    elseif V(i)<0 && V(i)>-5
        W(i) = V(i)^3;
    else
        W(i) = V(i);
    end

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MATLAB: Combine for loop and ~isinf,but there is an error in every loops except the result in the first loop

v = [3,6,1,Inf];
for k = 1:numel(v)
    n = v(k);
    z = n(~isinf(n)) 
end

displays:

z =  3
z =  6
z =  1
z = []

"i can't find where do i wrong"

Your code uses a scalar logical index:

~isinf(c(k))

Logical indexing is positional (it is not like subscript or linear indexing), so when you use a scalar logical index it acts only on the first element of the array, i.e. you either select the first element or you do not. That is exactly what your example output shows.

You cannot use a scalar logical index to work like a subscript and also expect it to select different elements of an array (i.e. not the first element). For that you would need to create a non-scalar logical index (normally these are the same size as the array being indexed) or use subscript/linear indexing first (which is what my answer does).

MATLAB: Matlab M-File

You should review the documentation on how to write a function, since your above code is not a correctly written function. First, come up with a name for your function, e.g. myFunction. Then create a new file called myFunction.m somewhere on the MATLAB path (e.g. your working directory). Then in that file put your code. E.g.,

function result = myFunction(V)
result = V;  % <-- allocate the result variable, copying all elements
%

% Insert your code here to create the result variable from the V variable
%
return
end

I will give you some hints about correcting your code:

Change this loop:

for i=1:1:6;  % <-- hard coded for exactly 6 elements

to this

for i=1:numel(V)  % <-- allows any size input

The following test has an error in the logic (compare this carefully with the requirement):

if [V(i)<0 | mod(V(i),2)==0 | mod(V(i),4)==0]

The following line has an error on the right hand side calculation (compare this carefully with the requirement):

    V(i)=i*i;

If you don't see what the errors are, step through a small example by hand and compare that to the code result. E.g., at the command line type this:

V=[10,4,7,-8,-3,-12];
myFunction(V)

Best Answer

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MATLAB: Combine for loop and ~isinf,but there is an error in every loops except the result in the first loop

MATLAB: Matlab M-File

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