June 2010 - GiNaC-list

is ginac thread safe for this case?
by Cristobal Navarro 26 Jul '10

26 Jul '10

will ginac be thread safe for this case? 1) threads access diferent expressions which are independant 2) each thread will increase the expression its working in.. for example thread1...expression1 += x+y thread2.... expression2 += 2*x.... and so on. 2) no function evaluation is done never. 3) however, all expressions share the same global symbols ( eg, expressions made of global symbols x and y ). 4) threads access the same common matrix of expressions, but two threads will never access the same cell. i'am testing at the moment, and is working but in the long run i am not sure if problems will arise. any information, welcome. thanks in advance. Cristobal <http://www.youtube.com/neoideo>

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parser and subs problem
by Felipe Bordeu 29 Jun '10

29 Jun '10

Hello, I'm trying to use the ginac parser, but doesn't work as expected. Page 81 of GiNaC 1.5.7 (an open framework ...) tutorial (29 march 2010) " It’s also possible to map input (sub)strings to arbitrary expressions: GiNaC::symbol x, y; GiNaC::symtab table; table["x"] = x+log(y)+1; GiNaC::parser reader(table); GiNaC::ex e = reader("5*x^3 - x^2"); " but I get the error terminate called after throwing an instance of 'std::invalid_argument' what(): find_or_insert_symbol: name "x" does not correspond to a symbol Abandon function find_or_insert_symbol in file ginac/parser/parse_context.cpp:49 can handle only symbols not expressions. So I tried to use only symbols and then do some subs to get the correct expression without success. GiNaC::symbol x, y; GiNaC::ex expr1 = x*y; GiNaC::ex mat1 = GiNaC::symbolic_matrix(2, 2, "K"); GiNaC::ex mat2 = GiNaC::symbolic_matrix(2, 2, "T"); GiNaC::ex expr2 = expr1.subs(GiNaC::lst(x==mat1,y==mat2)); cout << expr2 << endl; cout << expr2.evalm() << endl; and I get the error : [[K00,K01],[K10,K11]]*[[T00,T01],[T10,T11]] terminate called after throwing an instance of 'std::runtime_error' what(): matrix::mul_scalar(): non-commutative scalar Abandon do I have to use indexed objects to get the correct answer??? Thanks -- Felipe

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1by1 matrix to scalar
by Felipe Bordeu 23 Jun '10

23 Jun '10

Hello, I have a little problem, I'm dealing functions made of matrix products. My question is, how can "force" ginac to convert automatically all the 1by1 matrices to scalars?. or do I have to do it manually?? Here is a simple example. void main2(){ ex m1=symbolic_matrix(1, 3, "x"); ex m2=symbolic_matrix(3, 1, "y"); cout << m1 << std::endl; cout << m2 << std::endl; ex m3 = (m1*m2).evalm(); cout << m3 << std::endl; cout << ex_to<matrix>(m3)(0,0)<< std::endl;; ex m4 = m3-ex_to<matrix>(m3)(0,0); cout << m4 << std::endl; }; the output : [[x0,x1,x2]] [[y0],[y1],[y2]] [[y1*x1+y2*x2+y0*x0]] y1*x1+y2*x2+y0*x0 -y1*x1+[[y1*x1+y2*x2+y0*x0]]-y2*x2-y0*x0 the last line "should" be zero ?-- thanks Felipe

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writing symbols and expressions into binary files
by Cristobal Navarro 13 Jun '10

13 Jun '10

Hello, is it possible to write ginac symbols and expressions into a file as binary format?? i've tried this but i get segmentation fault when printing the read variables. you can try this one file example to see the problem. it writes to example.dat as binary format, then reads from it as binary format too. //CODE #include <ginac/ginac.h> #include <iostream> #include <fstream> using namespace std; using namespace GiNaC; int main(){ //WRITE if(1){ symbol a("a"), b("b"); ex myExp = a*b; cout << "Original: Symbols are '" << a << "' and '" << b << "', myExp = " << myExp << endl; fstream fw; fw.open( "example.dat", ios::out|ios::binary ); if( fw.is_open() ){ fw.write( (char*)&a, sizeof(a) ); fw.write( (char*)&b, sizeof(b) ); fw.write( (char*)&myExp, sizeof(myExp) ); fw.close(); } else{ printf("Error Opening File for writing\n"); } } //READ (SHOULD NOT DEPEND OF WRITE CODE) if(1){ symbol ca, cb; ex copyExp; fstream fr; fr.open( "example.dat", ios::in|ios::binary ); if( fr.is_open() ){ fr.read( (char*)&ca, sizeof(ca) ); fr.read( (char*)&cb, sizeof(cb) ); fr.read( (char*)&copyExp, sizeof(copyExp) ); fr.close(); cout << "Read from file: Symbols are '" << ca << "' and '" << cb << "' myExp = " << copyExp << endl; } else{ cout << "Error opening file for reading: does it exist?" << endl; } } return 1; } //CODE thanks in advance -- Cristobal <http://www.youtube.com/neoideo>

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implicit differentiation
by Felipe Bordeu 02 Jun '10

02 Jun '10

Hi everyone, I created a class for GiNaC to treat implicit differentiation, here is an example: symbol x = get_symbol("x"); ----> I use a factory ex A = dersymbol("A").dependent_of(x); -----> my new class, and I tell that is dependent of x ex dAdx = A.diff(x); cout << A << endl; -----> "A(x)" cout << "dA/dx : " << dAdx ; -----> "A(x)_1x" cout << "d2A/dx2 : " << dAdx.diff(x) ; -----> "A(x)_2x" cout << "dA/dy : " << A.diff(get_symbol("y")) ; -----> "0" Inside dersymbol I store the dependents variables and the degree of the differentiation. now my problem is that I what to make the substitution of A to something else, like x^2: cout << "dA/dx with A=x^2 is : " << dAdx.subs(A==pow(x,2)) << endl; (I know that the previous line is not correct) to get something like : "2*x" Any ideas?? Thanks (first time in this mailing list) Felipe

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Term ordering and compiling C++ code
by Doug 02 Jun '10

02 Jun '10

Hi, I'm running into a term ordering problem like the one mentioned in this post. http://permalink.gmane.org/gmane.comp.mathematics.ginac.general/1107 Relevant details about my application are below, for the curious. The short of it, though, is that the C++ code I am generating with ginac is so large (50MB) that the compiler can't handle it, and moreover, the values being represented by ginac symbols are array accesses that the compiler can't optimize away. So I need to create temporary values and do sub-expression elimination on the C++ code just so the compiler can have a chance. I have successfully done this using search-and-replace on the C++ code for other applications, but I guess I was just lucky that ginac printed terms in a consistent order. Is this a problem other ginac users have confronted? From the answer to the above post, it sounds like I need to write my own print function that can ensure expressions are printed in a predictable order. It looks like I can also inspect the expression tree and possibly do a proper job of common sub-expression elimination. But if there is an easier approach, I'd be very grateful for a pointer or two. Thanks, Doug Baker ------------------- Background Details ------------------- My application is related to visual odometry. I am computing the gradient and hessian for a function of 10 variables that involves converting quaternions to rotation matrices, applying those matrices to 3D points and projecting those points onto a 2D plane. I am generating code with ginac that is initially 50MB of C++ code. (And thank you for ginac being able to handle that monstrosity with such grace.) The input symbols are all array elements (e.g. symbol x("state[t+X]")) or function calls (e.g. symbol rTi11("rTi.getValue<1,1>()")). If I take the printed output from ginac as is, the C++ compiler can't properly optimize it because it doesn't know that state[t+X] is a constant or that getValue is constant. Moreover, the expressions have huge repeated expressions, and these bog the compiler down, too. I've been able to use a simple search-and-replace approach in other problems, and on this one that same approach has gotten me from 50MB to 6MB or so, but the term ordering issue is biting me now. For example, I have one sum (a+b+c+d) that occurs 232608 times. But there are 4! = 24 permutations of that sum that I'd have to replace. It's worse than that, though, because that's not the only expression like it. Some are bigger, like this: (-2.0*sK/sKSIJ+4.0*sK*sS2/pKSIJ2+-4.0*sI*sJ*sS/pKSIJ2). This has something like 72 permutations, not even counting the permutations of pKSIJ and pKSIJ2, which are themselves expressions like (a+b+c+d). And not only are there variations on this due to term ordering, similar expressions occur with different variables (e.g. with sJ instead of sK, etc.) So when all these expressions can be output in various orders, it's no longer feasible to generate all the permutations for search-and-replace. Support NPR 20 seconds at a time. www.twentysecondsatatime.org

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