decrease by 2/by 2 times

[arte-semaki]

Do I understand the following phrases correctly?
"Let's decrease the variable x by 2" means x:=x-2
"Let's decrease the variable x by 2 times" means x:=x/2

 

[JulianStuart]

Where have you seen these?
The first one sounds fine.

The second one does not.

You might try to wade through this thread about the use of "times" in such sentences...
three times longer than=three times as long as?

 

[arte-semaki]

Where have you seen these?

I have seen the expression "decrease something by a factor of", but I thought it was equivalent to "decrease something by X times". Is it wrong?

 

[JulianStuart]

I have seen the expression "decrease something by a factor of", but I thought it was equivalent to "decrease something by X times". Is it wrong?

"decrease something by a factor of" sounds normal and unambiguous. Where have you seen "decrease something by X times" ?

 

[arte-semaki]

Where have you seen "decrease something by X times" ?

It is the direct translation of the phrase "decrease something by a factor of" from the russian language.

 

[JulianStuart]

I have seen it in English but don't like it Others may feel it's OK. What's wrong with "by a factor of X"?

 

[Keith Bradford]

You can't decrease anything by a factor of anything.

If you decrease twenty by three, you have seventeen. That is certain.
But if you decrease twenty by a half you have either 19.5 or ten, who knows?
If you decrease twenty by a factor of five, you have... what? Four? Fifteen? Sixteen...???

 

[arte-semaki]

What's wrong with "by a factor of X"?

The phrase is longer than "by X times".

 

[JulianStuart]

The phrase is longer than "by X times".

Oh, dear