Re: Assertions in Mathematica?

*To*: mathgroup at smc.vnet.net*Subject*: [mg113447] Re: Assertions in Mathematica?*From*: "Nasser M. Abbasi" <nma at 12000.org>*Date*: Fri, 29 Oct 2010 06:27:35 -0400 (EDT)*References*: <iabc4e$5hg$1@smc.vnet.net>*Reply-to*: nma at 12000.org

On 10/28/2010 1:26 AM, kj wrote: > What's the best to implement assertions in Mathematica? By assertions > I mean statements like assert(exp) in C, which generate an error > if exp evaluates to false. > > This *should* be trivial, but it's Mathematica, so... > > Naively, I tried defining: > > Assert[exp_, msg__] := If[!exp, Message[msg]; Abort[]] > Hello KJ; May be a build-in Assert function would be nice. But what I do now is simply check, at the start of the function, manually, using an If[] statement, on all the "asserts" or conditions that I want satisfied, and if a condition fail, I Throw a message. Nothing fancy, but it works well, and it seems to satisfy the need of what Assert is supposed to do? Here is an example code I just wrote last night for a school HW, I was making a function to check for DD matrix and wanted to make sure the matrix was square, so wanted to assert that a matrix is square, and I looked to see if there was a MatrixSquareQ built-in Mathematica, but there was not, so I typed: ---------------------- diagonalDominantMatrixQ[mat_?(MatrixQ[#]&):=Module[{nRow,nCol}, {nRow,nCol}=Dimensions[mat]; (* assert matrix is square *) If[nRow!= nCol, Throw["diagonalDominantMatrixQ:: Matrix must be square"] ]; .... ] ----------------------- How is something like the above different from saying Assert[matrixIsSquare[mat]==True, error.....] in terms of its final effect it will have on behavior of program? aren't these equivalent? > ...which, of course, failed to work (as I've learned to expect); > instead it produced a cryptic error "Message::name : Message name > ... is not of the form symbol::name or symbol::name::language." > > I tried many other things, but after wasting 1 hour on this > ridiculously trivial programming task, I'm reduced to begging for > help. (This, by the way, is always the way it is with me and > Mathematica, and I've been using it on-and-off for almost 20 years. > The documentation is as useless to me today as it was 20 years ago. > I find it as horrible as the rest of Mathematica is brilliant.) > > I've posted desperate questions over programming mind-numbing > trivialities like this one in Mathematica before, i.e. questions > that seem so elementary and fundamental that no one who has access > to the documentation and who can read should *ever* have to ask > them. I ask them less wanting to get the answer to the questions > themselves than hoping to learn how I could have answered such > questions by myself. But I've never found how to do this. Those > who know the answers *already* can give them to me if they feel so > inclined. (And how they got to know the answer to begin with, I > don't know; I imagine it took years of sustained Mathematica > programming. Or maybe they asked a similar question before to > someone who already knew the answer...) But no one has been able > to tell me how someone who *doesn't* know the answers to such questions > already can figure it out without outside help. > > But hope springs eternal! If someone is kind enough to tell me > how I could implement my Assert, I'd be most grateful. If someone > can tell me how I could have arrived at this answer by myself by > consulting the documentation, I'd be ecstatic. > > TIA, > > kj > --Nasser