undefined variable, passive variable vector
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HELLO do you know how should i make vector with passiv variable.and be aware of that the size of this vector will be defined in the middel of program. thanks
1 个评论
David Young
2011-3-1
Please would you delete the four duplicates of this question. Thanks.
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Walter Roberson
2011-3-2
1 个投票
A = sym('A', [m n]) creates a m-by-n matrix of symbolic variables. The dimensions m and n of a matrix must be integers. You can use this syntax to create a 1-by-n or an n-by-1 vector. The sym function does not allow you to use symbolic variables without assigned numeric values as dimensions. By default, the generated names of elements of a vector use the form Ak, and the generated names of elements of a matrix use the form Ai_j. The base, A, must be a valid variable name. (To verify whether the name is a valid variable name, use isvarname). The values of k, i, and j range from 1 to m or 1 to n. To specify other form for generated names of matrix elements, use '%d' in the first input. For example, A = sym('A%d%d', [3 3]) generates the 3-by-3 symbolic matrix A with the elements A11, A12, ..., A33
3 个评论
kaveh
2011-3-3
kaveh
2011-3-3
Walter Roberson
2011-3-3
I do not know which version the ability to use a format with sym() came in. Which version are you running ?
更多回答（2 个）
David Young
2011-3-1
In MATLAB, you probably don't need to make the vector before you know its size. You don't have to declare variables, so the best solution is probably to simply not use the vector until the point where the size is known.
If there's some reason you need to reference the variable before that point, you could set it to the empty matrix:
v = [];
to indicate that it's a vector with, as yet, no contents.
3 个评论
kaveh
2011-3-1
David Young
2011-3-2
Can I just check - are you asking about the Symbolic Math Toolbox, as Kaustubha govind suggests? If you are, then sorry, I misunderstood. I don't know about that toolbox, and I hope someone else can help.
kaveh
2011-3-3
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