Opened 13 years ago

Closed 13 years ago

# basefield real: subst for parameters does not work

Reported by: Owned by: gorzel hannes minor 3-1-3 and higher singular-kernel 3-1-2

### Description

Compare:

```> ring r0 = (0,t),x,dp;
> poly f = tx+2;
> subst(f,x,1/2);
(1/2t+2)
> subst(f,t,1/2);   // OK in char 0 for parameters
1/2*x+2

> ring rr = (real,t),x,dp;
> poly f = tx+2;
> subst(f,x,1/2);
(2+t*0.5)
> subst(f,t,1/2);    // fails for parameters with real
? ringvar/par expected
? error occurred in or before STDIN line 10: `subst(f,t,1/2);`

```

### comment:1 Changed 13 years ago by hannes

Resolution: → invalid new → closed

This is as it should be:

```ring rr = (real,t),x,dp;
rr;
//   characteristic : 0 (complex:6 digits, additional 6 digits)
//   1 parameter    : t
//   minpoly        : (t^2+1)
//   number of vars : 1
//        block   1 : ordering dp
//                  : names    d
//        block   2 : ordering C
```

and one should not be able to substitute sqrt(-1) by 1/2.

Last edited 13 years ago by hannes (previous) (diff)

### comment:2 Changed 13 years ago by gorzel

War mir bisher nicht bekannt, dass real mit Parameter sich automatisch wie complex verhaelt.

```> ring rr = (real,t),x,dp;
> rr;
//   characteristic : 0 (complex:6 digits, additional 6 digits)
//   1 parameter    : t
//   minpoly        : (t^2+1)
//   number of vars : 1
//        block   1 : ordering dp
//                  : names    x
//        block   2 : ordering C
> ring rc = complex,x,dp;
> rc;
//   characteristic : 0 (complex:6 digits, additional 6 digits)
//   1 parameter    : i
//   minpoly        : (i^2+1)
//   number of vars : 1
//        block   1 : ordering dp
//                  : names    x
//        block   2 : ordering C
> ring rct = (complex,t),x,dp;
> rct;
//   characteristic : 0 (complex:6 digits, additional 6 digits)
//   1 parameter    : t
//   minpoly        : (t^2+1)
//   number of vars : 1
//        block   1 : ordering dp
//                  : names    x
//        block   2 : ordering C
}

This feature is not explained in the manual.
http://www.singular.uni-kl.de/Manual/latest/sing_29.htm#SEC39
```
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