Re: [sage-support] strange behavior in matrix substitution
On Jun 12, 2010, at 17:27 , Byungchul Cha wrote: Please tell me if this is a bug, or, I'm missing something obvious... sage: a = 3 # Assign a value to a variable a sage: b = a # Create a copy of a You're not really copying a, you're just making 'b' refer to the same thing that 'a' does, i.e. '3'. sage: b = 2 # Change the value of b Now b points to a different integer (2). sage: b 2 sage: a # The value of a remains unchanged, as expected. 3 So far, it looks good to me. But, when I do a similar thing with matrices, it doesn't look to be the same. sage: v = matrix(ZZ, 3, range(9)) sage: u = v u and v point to the same thing. sage: u[2] = [0,0,0] The matrix stored in the variable u has not been reassigned, it' been mutated. sage: u [0 1 2] [3 4 5] [0 0 0] sage: v [0 1 2] [3 4 5] [0 0 0] Shouldn't the value of v remain the same? Why does the change in u (or, a row of u) affect v? On Jun 12, 2010, at 8:25 PM, Justin C. Walker wrote: On Jun 12, 2010, at 19:07 , William Stein wrote: On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 17:27 , Byungchul Cha wrote: [snip] Shouldn't the value of v remain the same? Why does the change in u (or, a row of u) affect v? [snip] For, e.g., integers, u=v means that the names u,v both refer to their own copies of the value in question. Are you sure??? I think you statement that u is a new copy is wrong. I bet u is v would still return true above. Picky picky picky. I was hoping to avoid a trip into the twisty maze of passages in language definition (all of which are subtly different :-}). But you are correct. u is v does return true and the two actually refer to the same (physical) value. And, if one variable is modified, this doesn't modify the other, or the value that both previously referred to. Actually, even in the case of integers, if you were to modify one, it would modify the other. Most object are (basically) immutable, so this doesn't come up. Assignment never copies, it only creates references. - Robert -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: Sage on iPhone - Re: [sage-support] strange behavior in matrix substitution
I check my student's worksheets (those they share) on my iPod Touch no problem from sagenb. The only problem is viewing a plot() in 3D as the jre is not supported on the iPod Touch's Safari. HTH, A. Jorge Garcia http://calcpage.tripod.com Teacher Professor Applied Mathematics, Physics Computer Science Baldwin Senior High School Nassau Community College -Original Message- From: William Stein wst...@gmail.com To: sage-support@googlegroups.com sage-support@googlegroups.com Sent: Sat, Jun 12, 2010 11:55 pm Subject: Sage on iPhone - Re: [sage-support] strange behavior in matrix substitution On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 20:30 , William Stein wrote: On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 19:07 , William Stein wrote: On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 17:27 , Byungchul Cha wrote: [snip] [snip] I find that hard to believe. I thought you had Sage running on all things digital... Your right that I could check it on my iPhone, but I was lazy. I'm working on building sage *on* my ipad bit haven't finished yet OK, that would be cool. Would one have to jailbreak to run it? Yes, unfortunately. Also there's no iPhone fortran (yet), so only parts of sage will build. I'll show you at MSRI at sage days 22... Justin -- Justin C. Walker, Curmudgeon at Large Institute for the Absorption of Federal Funds --- Like the ski resort full of girls hunting for husbands and husbands hunting for girls, the situation is not as symmetrical as it might seem. - Alan MacKay -- -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org -- William Stein Professor of Mathematics University of Washington http://wstein.org -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
[sage-support] strange behavior in matrix substitution
Please tell me if this is a bug, or, I'm missing something obvious... sage: a = 3 # Assign a value to a variable a sage: b = a # Create a copy of a sage: b = 2 # Change the value of b sage: b 2 sage: a # The value of a remains unchanged, as expected. 3 So far, it looks good to me. But, when I do a similar thing with matrices, it doesn't look to be the same. sage: v = matrix(ZZ, 3, range(9)) sage: u = v sage: u[2] = [0,0,0] sage: u [0 1 2] [3 4 5] [0 0 0] sage: v [0 1 2] [3 4 5] [0 0 0] Shouldn't the value of v remain the same? Why does the change in u (or, a row of u) affect v? -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] strange behavior in matrix substitution
On Jun 12, 2010, at 17:27 , Byungchul Cha wrote: Please tell me if this is a bug, or, I'm missing something obvious... sage: a = 3 # Assign a value to a variable a sage: b = a # Create a copy of a sage: b = 2 # Change the value of b sage: b 2 sage: a # The value of a remains unchanged, as expected. 3 So far, it looks good to me. But, when I do a similar thing with matrices, it doesn't look to be the same. sage: v = matrix(ZZ, 3, range(9)) sage: u = v sage: u[2] = [0,0,0] sage: u [0 1 2] [3 4 5] [0 0 0] sage: v [0 1 2] [3 4 5] [0 0 0] Shouldn't the value of v remain the same? Why does the change in u (or, a row of u) affect v? You might think the behavior should be the same, but that's not the case. Objects with structure (matrices, for example) are copied by reference, while things like integers, which have little or no structure (from the user's perspective at any rate) are copied by value. What that means is that, for matrices, u=v means that the names u,v now refer to the same Sage object, so when you modify one, you are modifying the other (since you are really modifying the underlying object). For, e.g., integers, u=v means that the names u,v both refer to their own copies of the value in question. This is, BTW, the way Python works, and Python is the language with which (most of) Sage is implemented. In case you didn't already know that :-} HTH. Justin -- Justin C. Walker, Curmudgeon at Large Director Institute for the Enhancement of the Director's income --- -- They said it couldn't be done, but sometimes, it doesn't work out that way. - Casey Stengel -- -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] strange behavior in matrix substitution
Hello, On Sat, Jun 12, 2010 at 5:27 PM, Byungchul Cha cha3...@gmail.com wrote: Please tell me if this is a bug, or, I'm missing something obvious... sage: a = 3 # Assign a value to a variable a sage: b = a # Create a copy of a This does not create a copy of a. When you do a = 3, this creates new object for the integer 3 and then makes a point to that object. When you do b = a, it makes b point to the object that you originally created. When you do b = 2, it makes a new object for the integer 2 and makes b point to that. Notice that you are never changing (mutating) any of the objects. So far, it looks good to me. But, when I do a similar thing with matrices, it doesn't look to be the same. ... Shouldn't the value of v remain the same? Why does the change in u (or, a row of u) affect v? Here, the line sage: u[2] = [0,0,0] change the object that u in referencing. Since u and v point to that same object (as above), you see the changes when you look at v. You can use copy() to actually make a copy of v: sage: sage: v = matrix(ZZ, 3, range(9)) sage: v = matrix(ZZ, 3, range(9)) sage: u = copy(v) sage: u[2] = [0,0,0] sage: u [0 1 2] [3 4 5] [0 0 0] sage: v [0 1 2] [3 4 5] [6 7 8] --Mike -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] strange behavior in matrix substitution
On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 17:27 , Byungchul Cha wrote: Please tell me if this is a bug, or, I'm missing something obvious... sage: a = 3 # Assign a value to a variable a sage: b = a # Create a copy of a sage: b = 2 # Change the value of b sage: b 2 sage: a # The value of a remains unchanged, as expected. 3 So far, it looks good to me. But, when I do a similar thing with matrices, it doesn't look to be the same. sage: v = matrix(ZZ, 3, range(9)) sage: u = v sage: u[2] = [0,0,0] sage: u [0 1 2] [3 4 5] [0 0 0] sage: v [0 1 2] [3 4 5] [0 0 0] Shouldn't the value of v remain the same? Why does the change in u (or, a row of u) affect v? You might think the behavior should be the same, but that's not the case. Objects with structure (matrices, for example) are copied by reference, while things like integers, which have little or no structure (from the user's perspective at any rate) are copied by value. What that means is that, for matrices, u=v means that the names u,v now refer to the same Sage object, so when you modify one, you are modifying the other (since you are really modifying the underlying object). For, e.g., integers, u=v means that the names u,v both refer to their own copies of the value in question. Are you sure??? I think you statement that u is a new copy is wrong. I bet u is v would still return true above. I can't check this now, since am on iPhone This is, BTW, the way Pythttp://www.cnn.com/2010/HEALTH/05/29/energy.boosters/hon works, and Python is the language with which (most of) Sage is implemented. In case you didn't already know that :-} HTH. Justin -- Justin C. Walker, Curmudgeon at Large Director Institute for the Enhancement of the Director's income --- -- They said it couldn't be done, but sometimes, it doesn't work out that way. - Casey Stengel -- -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org -- William Stein Professor of Mathematics University of Washington http://wstein.org -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] strange behavior in matrix substitution
On Jun 12, 2010, at 19:07 , William Stein wrote: On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 17:27 , Byungchul Cha wrote: [snip] Shouldn't the value of v remain the same? Why does the change in u (or, a row of u) affect v? [snip] For, e.g., integers, u=v means that the names u,v both refer to their own copies of the value in question. Are you sure??? I think you statement that u is a new copy is wrong. I bet u is v would still return true above. Picky picky picky. I was hoping to avoid a trip into the twisty maze of passages in language definition (all of which are subtly different :-}). But you are correct. u is v does return true and the two actually refer to the same (physical) value. And, if one variable is modified, this doesn't modify the other, or the value that both previously referred to. I can't check this now, since am on iPhone I find that hard to believe. I thought you had Sage running on all things digital... Justin -- Justin C. Walker, Curmudgeon-At-Large Institute for the Enhancement of the Director's Income When LuteFisk is outlawed, Only outlaws will have LuteFisk -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] strange behavior in matrix substitution
On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 19:07 , William Stein wrote: On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 17:27 , Byungchul Cha wrote: [snip] Shouldn't the value of v remain the same? Why does the change in u (or, a row of u) affect v? [snip] For, e.g., integers, u=v means that the names u,v both refer to their own copies of the value in question. Are you sure??? I think you statement that u is a new copy is wrong. I bet u is v would still return true above. Picky picky picky. I was hoping to avoid a trip into the twisty maze of passages in language definition (all of which are subtly different :-}). But you are correct. u is v does return true and the two actually refer to the same (physical) value. And, if one variable is modified, this doesn't modify the other, or the value that both previously referred to. I can't check this now, since am on iPhone I find that hard to believe. I thought you had Sage running on all things digital... Your right that I could check it on my iPhone, but I was lazy.I'm working on building sage *on* my ipad bit haven't finished yet Justin -- Justin C. Walker, Curmudgeon-At-Large Institute for the Enhancement of the Director's Income When LuteFisk is outlawed, Only outlaws will have LuteFisk -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org -- William Stein Professor of Mathematics University of Washington http://wstein.org -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] strange behavior in matrix substitution
On Jun 12, 2010, at 20:30 , William Stein wrote: On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 19:07 , William Stein wrote: On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 17:27 , Byungchul Cha wrote: [snip] [snip] I find that hard to believe. I thought you had Sage running on all things digital... Your right that I could check it on my iPhone, but I was lazy.I'm working on building sage *on* my ipad bit haven't finished yet OK, that would be cool. Would one have to jailbreak to run it? Justin -- Justin C. Walker, Curmudgeon at Large Institute for the Absorption of Federal Funds --- Like the ski resort full of girls hunting for husbands and husbands hunting for girls, the situation is not as symmetrical as it might seem. - Alan MacKay -- -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Sage on iPhone - Re: [sage-support] strange behavior in matrix substitution
On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 20:30 , William Stein wrote: On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 19:07 , William Stein wrote: On Saturday, June 12, 2010, Justin C. Walker jus...@mac.com wrote: On Jun 12, 2010, at 17:27 , Byungchul Cha wrote: [snip] [snip] I find that hard to believe. I thought you had Sage running on all things digital... Your right that I could check it on my iPhone, but I was lazy. I'm working on building sage *on* my ipad bit haven't finished yet OK, that would be cool. Would one have to jailbreak to run it? Yes, unfortunately. Also there's no iPhone fortran (yet), so only parts of sage will build. I'll show you at MSRI at sage days 22... Justin -- Justin C. Walker, Curmudgeon at Large Institute for the Absorption of Federal Funds --- Like the ski resort full of girls hunting for husbands and husbands hunting for girls, the situation is not as symmetrical as it might seem. - Alan MacKay -- -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org -- William Stein Professor of Mathematics University of Washington http://wstein.org -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
