MATLAB Answers


error sign not valid

Asked by Charlene
on 9 May 2013

I have this function

n = 1;
Product = 1;
while( Product < N )
Product = Product * (2*n);
n = n + 1;

and this error keeps on popping up Error: File: Untitled5.m Line: 5 Column: 9 The expression to the left of the equals sign is not a valid target for an assignment.

  1 Comment

For readability sake, I'm going to add this on here.

% this loop is used to find how many iterations are needed in the expression 2*4*6*...*2n in order to exceed a predetermined maximum.
Product = 1;       % variables initialized as one
while ( Product < N)      % N being a predetermined maximum
Product = Product * (2 * n);      % 2*4*6*...*2n until
n = n + 1;

it would be helpful to know what the rest of the program is doing outside of this function. Is N declared, if so, what is it declared as? Where does Line: 5 Column: 9 correspond within what you have?


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1 Answer

Answer by the cyclist
on 9 May 2013
 Accepted answer

That's not valid MATLAB syntax. In particular, the curly brackets shouldn't enclose the while loop. (You also used capital N where you had been using small n.)

Does this do what you intend?

n = 1;
Product = 1;
while( Product < n )
Product = Product * (2*n);
n = n + 1;


small n is treated as a multiplier onto the 2 whereas large N is used as a maximum value. with that change, you have the intended function. Sorry about the curly brackets, that was my suggestion, I'm used to C coding.

i ran this function in MATLAB with N=500; i received a value of 6 for n and a final product of 3840 showing that this function does work.

2 = 2              n=1  -> 1st iteration
      2*4 = 8            n=2  -> 2nd iteration
      2*4*6 = 48         n=3  -> 3rd iteration
      2*4*6*8 = 384      n=4  -> 4th iteration
      2*4*6*8*10 = 3840  n=5  -> 5th iteration
      and then n is incremented one more time before exiting the loop to give n=6. 

In this case you could use the expression "#iterations = n-1" after the loop and you would have your answer.

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