# Beginner needs help

**URL:** <https://community.wolfram.com/t/beginner-needs-help/2198>\
**Category:** Questions\
**Tags:** mathematica, calculus\
**Created:** [May 13, 2014, 11:26pm UTC](https://community.wolfram.com/t/beginner-needs-help/2198 "2014-05-13T23:26:01Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![bobbixler4](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@bobbixler4](https://community.wolfram.com/u/bobbixler4)\
**Post date:** [May 13, 2014, 11:26pm UTC](https://community.wolfram.com/t/beginner-needs-help/2198/1 "2014-05-13T23:26:01Z")

</div>

This is giving me a logical value for my boundary condition equations. It’s not solving my equations. Where did I go wrong?

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**Author:** ![sukrause](https://yyz1.discourse-cdn.com/wolfram/user_avatar/community.wolfram.com/sukrause/32/41348_2.png) [@sukrause](https://community.wolfram.com/u/sukrause)\
**Post date:** [May 14, 2014, 9:18pm UTC](https://community.wolfram.com/t/beginner-needs-help/2198/2 "2014-05-14T21:18:27Z")

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_ **it** _ can read

> …, z, {x,1,1},{y,1,1}]

not much space left. Take an unit square instead for the independent variables.

One gets explanations for the messages in the help ref/message/NDSolve/deqn, so a derivative on the boundary is not specified by

```auto
D[z[x,0],y]==0

```

because that gives True (z[x,0] does not depend on y), but using

```auto
(D[z[x,y],y]/.y->0)==0

```

if done so one has

```auto
In[108]:= NDSolveValue[{D[z[x, y], {x, 4}] + 

    2 D[z[x, y], {x, 2}, {y, 2}] + D[z[x, y], {y, 4}] == q/d,
  z[x, 0] == 0, 
  z[0, y] == 0, (D[z[x, y], y] /. y -> 0) == 
   0, (D[z[x, y], x] /. x -> 0) == 0 }, z, {x, 0, 1}, {y, 0, 1}]

During evaluation of In[108]:= NDSolveValue::ivone: Boundary values may only be specified for one independent variable. Initial values may only be specified at one value of the other independent variable. >>

```

now one reads ref/message/NDSolve/ivone and considers the type of the equation, especially it states

> The partial differential equation solver used by NDSolve is designed to solve initial value problems.

purely elliptic problems are not in the scope of NDSolve[], if I understand it right.

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<div class="post-metadata">

**Author:** ![bobbixler4](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@bobbixler4](https://community.wolfram.com/u/bobbixler4)\
**Post date:** [May 15, 2014, 1:32pm UTC](https://community.wolfram.com/t/beginner-needs-help/2198/3 "2014-05-15T13:32:06Z")

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Udo, thanks for taking the time to help me. That means a lot to me. I’ll just code these equations in a general purpose programming language.  
Bob.