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#### Search: #### At

Function: at (<expr>, [<eqn_1>, ..., <eqn_n>]) Function: at (<expr>, <eqn>) Evaluates the expression <expr> with the variables assuming the values as specified for them in the list of equations `[<eqn_1>, ..., <eqn_n>]` or the single equation <eqn>.

If a subexpression depends on any of the variables for which a value is specified but there is no atvalue specified and it cant be otherwise evaluated, then a noun form of the `at` is returned which displays in a two-dimensional form.

`at` carries out multiple substitutions in series, not parallel.

See also `atvalue`. For other functions which carry out substitutions, see also `subst` and `ev`.

Examples:

```          (%i1) atvalue (f(x,y), [x = 0, y = 1], a^2);
2
(%o1)                          a
(%i2) atvalue (diff (f(x,y), x), x = 0, 1 + y);
(%o2)                        @2 + 1
(%i3) printprops (all, atvalue);
!
d             !
--- (f(@1, @2))!       = @2 + 1
d@1            !
!@1 = 0```

2 f(0, 1) = a

```          (%o3)                         done
(%i4) diff (4*f(x, y)^2 - u(x, y)^2, x);
d                          d
(%o4)  8 f(x, y) (-- (f(x, y))) - 2 u(x, y) (-- (u(x, y)))
dx                         dx
(%i5) at (%, [x = 0, y = 1]);
!
2              d           !
(%o5)     16 a  - 2 u(0, 1) (-- (u(x, y))!            )
dx          !
!x = 0, y = 1```

There are also some inexact matches for `at`. Try `?? at` to see them.

```(%o1)                                true
(%i2) ```

### Related Examples

f: a0 + a1*s^2 + a2*s^6;

cond1: at(f,s=1)=0;

cond2: at(diff(f,s),s...

Calculate

##### at-pred-rat

rat((x^2-1)/(x-1))=x+...

Calculate

pi:3.141592654;

d:2.50;

v:0.25;

Calculate

##### at-rat

rat((x^4-x^3-11*x^2+9...

rat((2-x)/(x+1))*((3*...

rat((x^3+2*x^2+4*x+8)...

Calculate

##### at-cos-integrate

at(.16*(integrate((3 ...

Calculate

##### at-diff-plot3d f(x,y):= y^2 - x;

...

x1:2;

Calculate

##### at-diff

diff(v*e^(-at), e);

Calculate

##### at-diff-exp

p0(s)=s**4+2*s**2+2;

p1(s)=2*exp(-t*s);

p2(s)=exp(-2*t*s);

Calculate

##### at-block-coeff-expand-lhs-powerdisp-print-rhs-simp

block(print("========...

Calculate

##### at-rat

rat((x^4-x^3-11*x^2+9...

rat((2-x)/(x+1))*(3*x...

rat((x^3+2*x^2+4*x+8)...

Calculate 