An extra + sign added to the results of subst

07082017, 02:28 AM
Post: #1




An extra + sign added to the results of subst
From the examples I am going through, this one is for substitution:
The example says: subst( 2*x^2 – x, x = a + 3 ) returns 2*(a + 3)^2 – a – 3 but I'm getting: returns 2*(a + 3)^2 + – a – 3 Any idea why I am getting the "+  a" ? I realize it means the same thing as "a" but I don't know why the extra + is added. Thanks, Jim 

07082017, 08:02 PM
Post: #2




RE: An extra + sign added to the results of subst
(07082017 02:28 AM)Skyblues Wrote: From the examples I am going through, this one is for substitution: Without knowing why you are getting the extra +, I would just like to quibble with your assumption that +a is the same as a. Mathematically, perhaps, I can see why you might think so. But whenever I have written such maths, I have used +(a) or +(a+b), making it clear what is being added. I have always queried +a in documentation, because it looks too much like it is supposed to read +ca and c has been omitted in a typo. Furthermore, when reading +a it can be misread/misunderstood as "plus or minus a", unless you are familiar with what the result should be. (In the computer languages I am experienced in, there is only one "" which serves as both negate and subtract... + is not so confusing if the "" is a different negate symbol  but even if that is so in the code/calculation, its not always clear in the documentation). Stephen Lewkowicz (G1CMZ) 

07092017, 01:31 AM
(This post was last modified: 07092017 01:32 AM by Skyblues.)
Post: #3




RE: An extra + sign added to the results of subst
> I would just like to quibble with your assumption that +a is the same as a.
> Mathematically, perhaps, I can see why you might think so. I agree with you completely and the reason I said they were the same is because, mathematically, it is the same and, hence, the Prime is not giving incorrect result, just a bit unusual. > But whenever I have written such maths, I have used +(a) or +(a+b) Exactly and if the result had been shown with parentheses (as you point out) I woudn't have thought too much about it. I found it very confusing and almost missed it (it's pretty small). Actually, the "" sign before the 'a is a little higher than the "+' sign that comes before it so I had to really look at it to see if it was actually trying to imply +(a). I took a screen shot in a larger skin so you can see it. It's strange, for sure. Jim 

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