[ublas] bugfix for matrix operation /

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Mario Mulansky

17 Apr 2013 17 Apr '13

2:20 a.m.

Hi, I wanted to add an elementwise divide operations for ublas matrices using operator / Unfortunately, there is operator/ defined for matrix and integral types which hides any other operator definition (matrix_expression.hpp l. 3388) and thus makes it impossible to add this functionality. I would like to add an enable_if statement there that checks if the second argument is convertible to matrix::value_type, as is done for other operators. Who would be responsible for this small change? I can provide the according patch, it's almost trivial. Mario

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Steven Watanabe

17 Apr 17 Apr

3:16 a.m.

AMDG On 04/16/2013 07:20 PM, Mario Mulansky wrote:

...

Hi,

I wanted to add an elementwise divide operations for ublas matrices using operator /

I don't think that's such a great idea. Using regular operators for elementwise operations is likely to be surprising. i.e. if you can do (A / B) you should be able to do (A * B) as well, and it you be the inverse of A / B. But multiplication is defined for matrices and is *not* an elementwise operation. There is no way to define this that won't surprise someone. There's a good reason why uBlas doesn't provide these operators already and why MATLAB has a separate set of operators for elementwise operations.

...

Unfortunately, there is operator/ defined for matrix and integral types which hides any other operator definition (matrix_expression.hpp l. 3388) and thus makes it impossible to add this functionality. I would like to add an enable_if statement there that checks if the second argument is convertible to matrix::value_type, as is done for other operators. Who would be responsible for this small change? I can provide the according patch, it's almost trivial.

In Christ, Steven Watanabe

Michael Marcin

7 a.m.

On 4/16/2013 10:16 PM, Steven Watanabe wrote:

...

AMDG

On 04/16/2013 07:20 PM, Mario Mulansky wrote:

...
Hi,

I wanted to add an elementwise divide operations for ublas matrices using operator /

I don't think that's such a great idea. Using regular operators for elementwise operations is likely to be surprising. i.e. if you can do (A / B) you should be able to do (A * B) as well, and it you be the inverse of A / B. But multiplication is defined for matrices and is *not* an elementwise operation. There is no way to define this that won't surprise someone. There's a good reason why uBlas doesn't provide these operators already and why MATLAB has a separate set of operators for elementwise operations.

...
Unfortunately, there is operator/ defined for matrix and integral types which hides any other operator definition (matrix_expression.hpp l. 3388) and thus makes it impossible to add this functionality. I would like to add an enable_if statement there that checks if the second argument is convertible to matrix::value_type, as is done for other operators. Who would be responsible for this small change? I can provide the according patch, it's almost trivial.

FWIW eigen3 implements element wise operators by converting a matrix representation to an array representation and doing operators there. Vector4f a, b, c; c = a.array() * b.array(); or c = a.array().abs().pow(3) * b.array().abs().sin(); where every operation is an element wise. Naturally this uses TMP so .array() doesn't make a copy or anything silly.

Mario Mulansky

2:08 p.m.

On Tuesday, April 16, 2013 08:16:57 PM Steven Watanabe wrote:

...

AMDG

On 04/16/2013 07:20 PM, Mario Mulansky wrote:

...
Hi,

I wanted to add an elementwise divide operations for ublas matrices using operator /

I don't think that's such a great idea. Using regular operators for elementwise operations is likely to be surprising. i.e. if you can do (A / B) you should be able to do (A * B) as well, and it you be the inverse of A / B. But multiplication is defined for matrices and is *not* an elementwise operation. There is no way to define this that won't surprise someone. There's a good reason why uBlas doesn't provide these operators already and why MATLAB has a separate set of operators for elementwise operations.

uh wait, i dont want to add this operator to ublas. I need it within odeint and it would be part of some ublas_extension.hpp in odeint, it would be merely an implementation detail no user would encounter. The problem is just that currently any definition of operater/ for two matrices is hidden by the ublas implementation of matrix-skalar division. So I would like to add an enabler to this, just as it is already there for the multiplication operator *, for example.

...

...
Unfortunately, there is operator/ defined for matrix and integral types which hides any other operator definition (matrix_expression.hpp l. 3388) and thus makes it impossible to add this functionality. I would like to add an enable_if statement there that checks if the second argument is convertible to matrix::value_type, as is done for other operators. Who would be responsible for this small change? I can provide the according patch, it's almost trivial. In Christ, Steven Watanabe

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Jeffrey Lee Hellrung, Jr.

4:06 p.m.

On Wed, Apr 17, 2013 at 7:08 AM, Mario Mulansky wrote:

...

On Tuesday, April 16, 2013 08:16:57 PM Steven Watanabe wrote:

...
AMDG

On 04/16/2013 07:20 PM, Mario Mulansky wrote:

...
Hi,

I wanted to add an elementwise divide operations for ublas matrices using operator /

I don't think that's such a great idea. Using regular operators for elementwise operations is likely to be surprising. i.e. if you can do (A / B) you should be able to do (A * B) as well, and it you be the inverse of A / B. But multiplication is defined for matrices and is *not* an elementwise operation. There is no way to define this that won't surprise someone. There's a good reason why uBlas doesn't provide these operators already and why MATLAB has a separate set of operators for elementwise operations.

uh wait, i dont want to add this operator to ublas. I need it within odeint and it would be part of some ublas_extension.hpp in odeint, it would be merely an implementation detail no user would encounter.

[...] If no user would encounter it, why don't you just define and use a free function elementwise_divide? Why does it have to be named operator/? - Jeff

Mario Mulansky

4:13 p.m.

On Wednesday, April 17, 2013 09:06:35 AM Jeffrey Lee Hellrung, Jr. wrote:

...

On Wed, Apr 17, 2013 at 7:08 AM, Mario Mulansky wrote:

...
On Tuesday, April 16, 2013 08:16:57 PM Steven Watanabe wrote:

...
AMDG

On 04/16/2013 07:20 PM, Mario Mulansky wrote:

...
Hi,

I wanted to add an elementwise divide operations for ublas matrices

using

...
...
operator /

I don't think that's such a great idea. Using regular operators for elementwise operations is likely to be surprising. i.e. if you can do (A / B) you should be able to do (A * B) as well, and it you be the inverse of A / B. But multiplication is defined for matrices and is *not* an elementwise operation. There is no way to define this that won't surprise someone. There's a good reason why uBlas doesn't provide these operators already and why MATLAB has a separate set of operators for elementwise operations.

uh wait, i dont want to add this operator to ublas. I need it within odeint and it would be part of some ublas_extension.hpp in odeint, it would be merely an implementation detail no user would encounter.

[...]

If no user would encounter it, why don't you just define and use a free function elementwise_divide? Why does it have to be named operator/?

oh because then i can reuse my code that is based on operator / being defined, it's just the easier way for me to go. but despite that i consider it a bug in ublas. the templated operator matrix/skalar gets instantiated even if i write matrix/matrix. this then results in a nasty compiler error instead of telling me operator/ for matrix matrix is not defined, as it would if the enable_if was there. best, mario

...

- Jeff

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Mario Mulansky

20 Apr 20 Apr

5:02 p.m.

On Tuesday, April 16, 2013 08:16:57 PM Steven Watanabe wrote:

...

AMDG

On 04/16/2013 07:20 PM, Mario Mulansky wrote:

...
Hi,

I wanted to add an elementwise divide operations for ublas matrices using operator /

I don't think that's such a great idea. Using regular operators for elementwise operations is likely to be surprising. i.e. if you can do (A / B) you should be able to do (A * B) as well, and it you be the inverse of A / B. But multiplication is defined for matrices and is *not* an elementwise operation. There is no way to define this that won't surprise someone. There's a good reason why uBlas doesn't provide these operators already and why MATLAB has a separate set of operators for elementwise operations.

So here's the patch I would like to be applied to ublas. As I said, it's almost trivial and would allow to add matrix-matrix operator/ for those who want it. Is it possible to have that added to ublas? Best, Mario

...

...
Unfortunately, there is operator/ defined for matrix and integral types which hides any other operator definition (matrix_expression.hpp l. 3388) and thus makes it impossible to add this functionality. I would like to add an enable_if statement there that checks if the second argument is convertible to matrix::value_type, as is done for other operators. Who would be responsible for this small change? I can provide the according patch, it's almost trivial. In Christ, Steven Watanabe

_______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

Jeffrey Lee Hellrung, Jr.

22 Apr 22 Apr

1:57 a.m.

On Sat, Apr 20, 2013 at 10:02 AM, Mario Mulansky wrote:

...

On Tuesday, April 16, 2013 08:16:57 PM Steven Watanabe wrote:

...
AMDG

On 04/16/2013 07:20 PM, Mario Mulansky wrote:

...
Hi,

I wanted to add an elementwise divide operations for ublas matrices using operator /

I don't think that's such a great idea. Using regular operators for elementwise operations is likely to be surprising. i.e. if you can do (A / B) you should be able to do (A * B) as well, and it you be the inverse of A / B. But multiplication is defined for matrices and is *not* an elementwise operation. There is no way to define this that won't surprise someone. There's a good reason why uBlas doesn't provide these operators already and why MATLAB has a separate set of operators for elementwise operations.

So here's the patch I would like to be applied to ublas. As I said, it's almost trivial and would allow to add matrix-matrix operator/ for those who want it. Is it possible to have that added to ublas?

Better off creating a ticket and attaching the patch. - Jeff

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participants (4)

Jeffrey Lee Hellrung, Jr.
Mario Mulansky
Michael Marcin
Steven Watanabe