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Not sure if this question belongs in this form but I don't know where else to go. I'm trying to index a matrix and do a < comparison on it. Every time I try something like A[1] it says:

Error, a Vector is not valid lhs to < or <=.

Can anyone help?

EXAMPLE:

A:=<1,2,3>:

b:=A[2]:

if b < 2 then .....

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    A matrix is a two-dimensional array of numbers. Why are you providing only one index?2011-09-30
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    sorry. I reduce it down to a 1 dimensional 1x4 matrix (vector).2011-09-30
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    And what do you expect `<` to do on a vector? That's not usually defined.2011-09-30
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    What exactly did you feed Maple? If you don't show your exact input, none of us could be more helpful...2011-09-30
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    Adding to Henning's comment, you need to properly define < on vectors. For example, you can compare the n^th norms of vectors by _norm(A, n)_. Or you could compare the two vectors component-wise as follow. _C := zip((x,y) -> evalb(x < y), A, B);_ and then _andmap(\`=\`, C, true);_2011-10-01

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Which version of Maple are you using? For me, using Maple 12, the following works just fine:

A := <1,2,3>;

$$A := \begin{bmatrix}1 \\ 2 \\ 3\end{bmatrix}$$

b := A[2];

$$b := 2$$

is(b < 2);

$$false$$

is(b <= 2);

$$true$$

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    yea well thats what i was trying to do but for for some reason my if statement wouldn't work. give you credit anyways2011-10-04