7

2

An apostrophe `'`

is often used when we want to distinguish two variables. For example, if we already have a variable `t`

and we may want define another variable `t'`

. What I found weird is that, in *Mathematica` it is legitimate to define a variable with apostrophe but it just can't clear a variable which has an apostrophe in the usual way.

For example, if we write the following

```
t'=8
```

and `3t'`

will correctly give `24`

but `Clear[t']`

will prompt an error says

Clear::ssym: t' is not a symbol or a string

Can anyone help?

6Apostrophe means

`Derivative`

in Mathematica. You don't define a new variable, you add a rule for`Derivative`

function. It is not`Protected`

, which is why you can do it. Don't use apostrophe for this purpose, this is a wrong thing to do. – Leonid Shifrin – 2012-12-03T13:59:40.4201@NasserM.Abbasi It

isreally often used in mathmatics that way and I have seen people using this notation inMathematicavery often. I'm sure if someone uses this notation, he just tries it without looking it up in the documentation and since it seems to work, they think it's fine. – halirutan – 2012-12-03T14:50:04.5071

Duplicate of: http://mathematica.stackexchange.com/q/373/5

– rm -rf – 2012-12-03T16:21:40.757I have a question! why mathematica design Derivative to be not protected?? – matheorem – 2012-12-04T13:05:25.770