# [✓] Write a matrix multiplication with indefinite limits?

Posted 1 year ago
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 Hello, I need to find an answer to this problem. Let G(t) be a nxn matrix. I need to calculate G(t-1)xG(t-2)x...xG(2)xG(1) where x is the usual matrix multiplication. I can't use the function Product[G(i),{i,t-1,1}] because it uses the usual multiplication of real numbers. Any Idea of how can I solve this? Answer
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Posted 1 year ago
 The matrix multiplication is Dot in Mathematica. If you need your product for display only, you can inactivate it: Inactive[Dot][g[t - 1], g[t - 2], \[Ellipsis], g, g] If you need it for actual calculation you can use the infix form of Dot: g.g.g.g.g or generate the terms with Table: Dot @@ Table[g[k], {k, 5, 1, -1}] Answer
Posted 1 year ago
 I'm sorry, I guess I've not been clear. I need to calculate (not only for display) G(t-1)xG(t-2)x...xG(2)xG(1) without setting any value to t. For instance, the product x(x-1)...*(x-t) is equal to Gamma(x+1)/Gamma(x-t). I want to find a closed expression that would depend on t. Answer
Posted 1 year ago
 Hmmm. What do you mean by "closed expression"? Smile, make one of your own. Say your procuct is called U[t] and according to Gianlucas proposal you can write U[t_?NumericQ] := Dot @@ Table[g[j], {j, 1, t - 1}] You can use it everywhere: In:= U[t] Out= U[t] Whenever you need it mor explicit give it a t ( element of Integers) In:= U Out= g.g.g Answer
Posted 1 year ago
 Let me try to explain with an example: In:= Product[x - i, {i, 0, t - 1}] Out= (1 - t + x) Pochhammer[2 - t + x, -1 + t] what I need is the expression in "Out", this is what I mean by "closed expression". Look that the boundary I've used is an unapropriate bound to a Table or to a loop, but it's not to the function "Product". I'm looking for a function that would do the same thing as the function Product but instead of using the usual multiplication of real numbers, it uses the usual matrix product. Answer