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Re: [Boost-users] Equation idea (follow-up)
by Sohail Somani 05 Apr '06

05 Apr '06

Comments below > std::cout << a(_y is 5, _z is 10) << std::endl; I do think the idea of assigning inputs at the call site is important which is what you've done. It would be nice to use the named parameter library here if possible to get rid of the leading underscores. > class ArgTable I think this is not needed if you can use the named parameter library. > class Equation Should be templated I don't know what this offers over boost bind and function. I use these to do a lot of this type of stuff. As long as the number of parameters are low, its easy to understand and you get some currying for free. SomeFn f = bind(my_fn(),_1,_2); // its not too difficult to understand this as x,y // I'd really like to do double v = f(x=x,y=y); Sohail

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Re: [Boost-users] Equation idea (follow-up)
by Stephen Gross 05 Apr '06

05 Apr '06

>Why don't just use Blitz++ for various expressions/equations? ;) I didn't know about blitz++, but I've just now taken a quick look at it. It appears designed for performance above all, which is not the idea behind my equation toolkit. The equation toolkit is designed to let you *easily* write straight-forward equations, combine them, and re-assign them as you want. For instance: ================= Equation e = x + y print e(x -> 1, y -> 2) e = y print e(y -> 9) e = z + 2 * y / a + b print e(a -> 2, b -> 5, y -> 100, z -> 50) ================= The advantage is that you can easily change an equation so you don't actually have to write functions for each equation. If you have a situation where you need to dynamically change around equations a lot during runtime, this system should (ideally) be useful. --Steve

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Equation idea (follow-up)
by Stephen Gross 05 Apr '06

05 Apr '06

Ok, at least one person said they were interested in seeing my idea for an equation toolkit, so here goes... The files a few hundred lines, so hopefully that's ok for this group. If I've exceed some message size, I'm sorry in advance... ======== e.cpp (client code) follows ========= #include "equation.h" #include "equation_enable_macros.h" int main() { equation::Equation a; a = _y + _z; std::cout << a(_y is 5, _z is 10) << std::endl; a = _x + 8 * (_y - _z); std::cout << a(_x is 2, _y is 3, _z is -9000.9) << std::endl; return 0; } ======== equation.h follows (the real work) ========= // Copyright Stephen Gross 2006 #ifndef api_equation #define api_equation #include <string> #include <iostream> #include <map> #include "boost/function.hpp" #include "boost/lambda/lambda.hpp" #include "boost/lambda/bind.hpp" namespace equation { class ArgTable { typedef std::map<std::string, double> MapType; public: ArgTable & setArg(const std::string & name, double val) { my_map[name] = val; return *this; } virtual double getArg (const std::string & name) const { MapType::const_iterator f = my_map.find(name); if(f == my_map.end()) { std::cout << "Error: Equation requested argument '" << name << "' which was not given." << std::endl; exit(0); } else { return f->second; } } private: MapType my_map; }; class ArgTableReporter : public ArgTable { public: virtual double getArg(const std::string & name) const { my_last_var = name; return 0; } const std::string & getLastVar() const { return my_last_var; } private: mutable std::string my_last_var; }; /// /// Represents an Equation, simply put. /// /// The idea here is that, for any Equation that takes named arguments ("x", "y", etc.) and manipulates them /// arithmetically, such an Equation can in fact be encapsulated in an Equation instance. /// /// class Equation { public: typedef boost::function1<double, const ArgTable &> FunctorType; /// @name Constructors //@{ Equation() : my_ftr(boost::lambda::constant(0)) { ; } Equation(const Equation & other) : my_ftr(other.my_ftr) { } template<typename T> Equation(const T & t) : my_ftr(t) { } //@} /// @name The underlying function that invokes the functor: //@{ double go (const ArgTable & args) const { return my_ftr(args); } //@} /// @name operator() //@{ double operator() () { return go(ArgTable()); } template<typename A1> double operator() (const A1 & a1, double v1) const { ArgTable args; ArgTableReporter names; a1(names); args.setArg(names.getLastVar(), v1); return go(args); } template<typename A1, typename A2> double operator() (const A1 & a1, double v1, const A2 & a2, double v2) const { ArgTable args; ArgTableReporter names; a1(names); args.setArg(names.getLastVar(), v1); a2(names); args.setArg(names.getLastVar(), v2); return go(args); } template<typename A1, typename A2, typename A3> double operator() (const A1 & a1, double v1, const A2 & a2, double v2, const A3 & a3, double v3) const { ArgTable args; ArgTableReporter names; a1(names); args.setArg(names.getLastVar(), v1); a2(names); args.setArg(names.getLastVar(), v2); a3(names); args.setArg(names.getLastVar(), v3); return go(args); } template<typename A1, typename A2, typename A3, typename A4> double operator() (const A1 & a1, double v1, const A2 & a2, double v2, const A3 & a3, double v3, const A4 & a4, double v4) const { ArgTable args; ArgTableReporter names; a1(names); args.setArg(names.getLastVar(), v1); a2(names); args.setArg(names.getLastVar(), v2); a3(names); args.setArg(names.getLastVar(), v3); a4(names); args.setArg(names.getLastVar(), v4); return go(args); } //@} private: FunctorType my_ftr; }; namespace Private { class Sigma { public: Sigma() : my_start(0), my_stop(0), my_iter(boost::lambda::constant(0.0)) { } Sigma(double start, double stop, const Equation & eq) : my_start((int)start), my_stop((int)stop), my_iter(eq) { } Sigma(const Sigma & other) : my_start(other.my_start), my_stop(other.my_stop), my_iter(other.my_iter) { } Sigma& operator=(const Sigma & other) { if(this != &other) { my_start = other.my_start; my_stop = other.my_stop; my_iter = other.my_iter; } return *this; } double go (const ArgTable & args) const { ArgTable newargs = args; double result = 0.0; for(int i = my_start; i <= my_stop; ++i) { newargs.setArg("i", (double)i); result += my_iter.go(newargs); } return result; } private: int my_start; int my_stop; Equation my_iter; }; /// /// Helper struct so that unary math functions can be easily macro-ified for constructing Equations. struct UnaryFunc { UnaryFunc(double (*fn) (double), const Equation::FunctorType & arg_getter) : my_fn(fn), my_arg_getter(arg_getter) { } UnaryFunc(double (*fn) (double), double v) : my_fn(fn), my_arg_getter(boost::lambda::constant(v)) { } UnaryFunc(const UnaryFunc & other) : my_fn(other.my_fn), my_arg_getter(other.my_arg_getter) { } UnaryFunc& operator=(const UnaryFunc & other) { if(this != &other) { my_fn = other.my_fn; my_arg_getter = other.my_arg_getter; } return *this; } double go(const ArgTable & args) const { return (*my_fn) (my_arg_getter(args)); } double (*my_fn) (double); Equation::FunctorType my_arg_getter; }; /// /// Helper struct so that binary math functions can be easily macro-ified for construction Equations. struct BinaryFunc { BinaryFunc( double (*fn) (double, double), const Equation::FunctorType & arg1_getter, const Equation::FunctorType & arg2_getter) : my_fn(fn), my_arg1_getter(arg1_getter), my_arg2_getter(arg2_getter) { } BinaryFunc( double (*fn) (double, double), double arg1, const Equation::FunctorType & arg2_getter) : my_fn(fn), my_arg1_getter(boost::lambda::constant(arg1)), my_arg2_getter(arg2_getter) { } BinaryFunc( double (*fn) (double, double), const Equation::FunctorType & arg1_getter, double arg2) : my_fn(fn), my_arg1_getter(arg1_getter), my_arg2_getter(boost::lambda::constant(arg2)) { } BinaryFunc( double (*fn) (double, double), double arg1, double arg2) : my_fn(fn), my_arg1_getter(boost::lambda::constant(arg1)), my_arg2_getter(boost::lambda::constant(arg2)) { } BinaryFunc(const BinaryFunc & other) : my_fn(other.my_fn), my_arg1_getter(other.my_arg1_getter), my_arg2_getter(other.my_arg2_getter) { } BinaryFunc& operator=(const BinaryFunc & other) { if(this != &other) { my_fn = other.my_fn; my_arg1_getter = other.my_arg1_getter; my_arg2_getter = other.my_arg2_getter; } return *this; } double go(const ArgTable & args) const { return (*my_fn) (my_arg1_getter(args), my_arg2_getter(args)); } double (*my_fn) (double, double); Equation::FunctorType my_arg1_getter; Equation::FunctorType my_arg2_getter; }; } // End namespace Private } // End namespace equation #define VAR(name) boost::lambda::bind<double>(&equation::ArgTable::getArg, boost::lambda::_1, std::string(#name)) #define EQ(name) boost::lambda::bind<double>(&equation::Equation::go, &name, boost::lambda::_1) #endif =========== equation_enable_macros.h follows ============ #ifndef api_equation_enable_macros #define api_equation_enable_macros // Disable macros now available: #undef api_equation_disable_macros #define is , #define _a VAR(a) #define _b VAR(b) #define _c VAR(c) #define _d VAR(d) #define _e VAR(e) #define _f VAR(f) #define _g VAR(g) #define _h VAR(h) #define _i VAR(i) #define _j VAR(j) #define _k VAR(k) #define _l VAR(l) #define _m VAR(m) #define _n VAR(n) #define _o VAR(o) #define _p VAR(p) #define _q VAR(q) #define _r VAR(r) #define _s VAR(s) #define _t VAR(t) #define _u VAR(u) #define _v VAR(v) #define _w VAR(w) #define _x VAR(x) #define _y VAR(y) #define _z VAR(z) #define _sigma(start, stop, iter) boost::lambda::bind<double> (&equation::Private::Sigma::go, equation::Private::Sigma (start, stop, iter), boost::lambda::_1) #define _sqrt(x) boost::lambda::bind<double> (&equation::Private::UnaryFunc::go, equation::Private::UnaryFunc (&sqrt, x), boost::lambda::_1) #define _pow(x, y) boost::lambda::bind<double> (&equation::Private::BinaryFunc::go, equation::Private::BinaryFunc (&pow, x, y), boost::lambda::_1) #endif ========= end of code snippets ==============

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Re: [Boost-users] equation (really expression) idea (follow-up)
by james.jones＠firstinvestors.com 05 Apr '06

05 Apr '06

From: "Stephen Gross" <sgross(a)darwin.epbi.cwru.edu> > Ok, at least one person said they were interested in seeing my idea for an > equation toolkit, so here goes... The files a few hundred lines, so > hopefully that's ok for this group. If I've exceed some message size, I'm > sorry in advance... This is a decent start, but I have several problems with it. 1. Types are not template-ized. I don't want everything to be a double. 2. Perhaps variables should be first-class objects, not just placeholders in BLL. 3. (Style not substance) Many of the type and function names aren't very clear. Examples: go() and MapType; I'm thinking the client syntax should be something more like this: expression expr; variable<double> x; variable<int> y; expr = x + y; double v = expr; // would throw because x and y are unassigned x = 10; y = 20; v = expr; // assigns 30 to v It would be cool to then be able to define some sort of 'evaluate' function so that you could write: v = expr.evaluate(10, 20); // v <- 30 Perhaps this is where the BLL comes in, because you'd first have to map the positional arguments to the variables in the expression. Maybe you could also extend this to handle currying. - James

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Problem with memory allocation in UBLAS matrix and vector
by Vasilios Papakos 05 Apr '06

05 Apr '06

Hello, Here is the problem I am having: In the following code (tried to keep it as short as possible), I create a vector [vec1] and a matrix [mat1] in the respective test functions. Then, I create [vec2] and [mat2] in main, but when I print them they have the values of [vec1] and [mat1]. Why is this happening? I am quite new to boost, so I may miss something quite fundamental. I really appreciate you help. System: Fedora Core 4, boost-1.33.1.-5, g++ 4.0.2 Regards, Vasilios ---------------------------------------------------------------------------------------------------------------------------------------------------------- #include <boost/numeric/ublas/vector.hpp> #include <boost/numeric/ublas/matrix.hpp> #include <boost/numeric/ublas/io.hpp> typedef boost::numeric::ublas::matrix<double> ublas_matrix; typedef boost::numeric::ublas::vector<double> ublas_vector; using std::cout; using std::endl; void test_matrix(); void test_vector(); int main() { test_matrix(); ublas_matrix mat2(3, 2); cout << "m2 = " << mat2 << endl; test_vector(); ublas_vector vec2(4); cout << "v2 = " << vec2 << endl; } void test_matrix() { unsigned m = 3, n = 2; ublas_matrix mat1(m, n); for (unsigned i = 0; i < m; ++ i) for (unsigned j = 0; j < n; ++ j) mat1(i, j) = 5.0; } void test_vector() { ublas_vector vec1(4); for (unsigned i = 0; i < vec1.size(); ++i) vec1(i) = i; } ----------------------------------------------------------------------------------------------------------------------------------------------------------

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Serialization: crash at launch of program (due to boost::serialization::base_object)
by RIVASSEAU Jean Noel 05 Apr '06

05 Apr '06

Hello, My program crashes at launch (not even a exit(0) as the first line of main(int argc, char *argv[]) will stop it from crashing), due to the BSL. What I am trying to do is: I have a class, whose serialization is split (eg, save and load functions are provided, and they are different). Now this class had a parent class, so I used to call boost::serialization::base_object<MObject>() on the base class MObject. However I want to change the parent of my class to a different class. I also want to update my old archives, so I decided to leave the load function of my class untouched, while I would change the save function, to update the call to base_object to the new parent class (not MObject anymore). I thought it would work, since it would load the old archive using the same method, but save it using the new, so I would have ran only one time the program and the archive would be updated (then, of course, before running it again I would have to recompile it one more time with the correct changes to the load function). But it does not work as expected, since it seems the BSL does not like the fact that save and load functions calls to boost::serialization::base_object do not specify the same base class. It does not complain at compile time but crashes at run time before even entering main and certainly before loading any archive. The crash is due to a NULL pointer, I have tried to debug with gdb but the crash apparently occurs on the _libkernel32_a_iname () so I do not not know where it is (too low level for me). Robert, do you have an idea what is going on? I suspect a bug - however if it is "normal" behaviour (I think it should then throw an exception rather than crash), do you have an idea how could I update my archives? I need to change the parent of this class, but need to be able to read my old archives - and changing them "by hand" by looking into the XML archive code is tool hard. Thank you, regards Jean-Noël Rivasseau

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Re: [Boost-users] Idea for equation library
by james.jones＠firstinvestors.com 05 Apr '06

05 Apr '06

Stephen Gross wrote: > The idea is that you can encapsulate an algebraic function in a standalone > 'Equation' instance, and dynamically reassign that equation. It's built off > of boost::lambda (of course), but it lets you name the variables rather than > just refer to them with the standard placeholders (_1, _2, etc.). Is it > worthwhile for me to post the toolkit code on this group? I'd love to see this. But it should be called "Expression", not "Equation" - the concepts you'd be creating aren't "equations". Equation: x + y = z Expression: x + y - James

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Confusion on The Directory Structure For serialization library
by Cheok Yan Cheng 05 Apr '06

05 Apr '06

You might thoroughly read http://www.boost.org/more/getting_started.html#Build_Install. Where under the Results section, the naming convention is described. -------------------------------------------------------- That's cool! I get the naming convention I want after running bjam install. Thank you very much! __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

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Boost.Filesystem
by Elisha Berns 05 Apr '06

05 Apr '06

I asked this two weeks ago but didn't get any reply: Can file locking and permission setting be added to Boost.Filesystem? Elisha Berns

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Re: [Boost-users] [Serialization] a newbie question about retrieving objects serialized through base class pointers
by t.sammoud 05 Apr '06

05 Apr '06

Robert Ramey wrote: >If BOOST_CLASS_EXPORT is used, the class name is included as an attribute in >the xml file. >Otherwise, the class_id variable - another xml attribute is used. This is >set/recovered by the >"registration" process. I understood from the documentation that BOOST_CLASS_EXPORT works for classes which derive from a virtual base class, which isn't really the case for me. Is it possible to add class names as attributes to xml archives even for classes which aren't serialized through base class pointers? If there is a way, this would really helps me Thanks Accédez au courrier électronique de La Poste : www.laposte.net ; 3615 LAPOSTENET (0,34 /mn) ; tél : 08 92 68 13 50 (0,34/mn)

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