# Emil Widmann's profile - activity

 2020-04-11 13:28:28 +0200 commented answer Substitute variable in differential equation Vielen Dank! I would upvote 2 times more if I could ... 2020-04-11 08:34:58 +0200 commented answer Substitute variable in differential equation Just 2 more questions: How do I insert latex code here in this forum? How are the symbols D0 and D0,0 defined (result from show(divG), divG in the first version as function from r)? 2020-04-11 07:38:56 +0200 commented answer substitute variable inside function great, thanks! 2020-04-11 07:00:22 +0200 commented answer Substitute variable in differential equation Thanks a lot for showing me. - I got the first term of the solution by hand, but missed the second. The result has a meaning, but what it is I have to figure out, it seems the bracket contains sort of a "density operator". 2020-04-10 18:53:00 +0200 asked a question substitute variable inside function I can do f(a,b) = a^2+b^3; f=f-f.subs(a=(a-1)) (a, b) |--> -(a - 1)^2 + a^2  I tried to write a function which does this for arbitrary expressions and variables def test(self, symb): return (self-self.subs(symb=(symb-1)))  but test(f,a) (a, b) |--> 0  fails miserably. It seems self.subs(symb=(symb-1)) can not be evaluated properly. How can I achieve what I want? 2020-04-08 11:07:00 +0200 asked a question Substitute variable in differential equation I have m = function('m')(r) V = function('V')(r) phi = m(r)/r V = 4*pi*r^3/3 divG = (diff(phi,r,2)+2/r*diff(phi,r)).full_simplify()  which describes a spherical symmetric source term of a field, nice. Now I want to get this as a function of volume, not of radius and tried: a=divG.subs(r=V(r))  But it gets me nowhere - It should also substitute the differentials - How to solve this? 2017-05-19 01:52:59 +0200 received badge ● Popular Question (source) 2014-01-09 22:19:21 +0200 received badge ● Famous Question (source) 2013-07-11 09:46:35 +0200 received badge ● Nice Question (source) 2012-12-06 13:11:54 +0200 marked best answer SAGE_FAT_BINARIES and SAGE_ATLAS_ARCH - compile for old processors Hi Emil, this is due to a logical bug in the atlas spkg: the system-wide variable SAGE_FAT_BINARY currently takes precedence over the specific variable SAGE_ATLAS_ARCH as explained in the trac ticket http://trac.sagemath.org/sage_trac/ti... A possible workaround until it is fixed is: cd \${YOUR_SAGE_ROOT}/spkg/standard/ tar xvf atlas-3.8.4.p1.spkg modify atlas-3.8.4.p1/spkg-install according to the proposed patch http://trac.sagemath.org/sage_trac/at... (this is around line 203). tar cvf atlas-3.8.4.p1.spkg atlas-3.8.4.p1 compile as usually exporting SAGE_FAT_BINARY='yes' and SAGE_ATLAS_ARCH='PIII' Ciao, Thierry 2012-12-06 13:11:54 +0200 received badge ● Scholar (source) 2012-12-06 13:11:49 +0200 commented answer SAGE_FAT_BINARIES and SAGE_ATLAS_ARCH - compile for old processors Hi Thierry - thanks for that explanation! I will keep this in mind and when the time is ripe I will update the Live CD accordingly... cheers emil 2012-12-05 13:23:12 +0200 asked a question SAGE_FAT_BINARIES and SAGE_ATLAS_ARCH - compile for old processors Hi, I recently compiled a new version of the Sage Live CD. In older versions it was enough to set SAGE_FAT_BINARIES='yes' to create a binary with low requirements on processor instructions (like "sse2" instruction set). In the newer versions I also used SAGE_ATLAS_ARCH='base' flag, but now I have a report that it is not working properly on an old pentium processor. I read something in the sage-devel group that there might be some interference between those build flags. What is the present procedure to produce a true "fat" binary which should run on possibly the widest range of hardware (without having to grant to use modern hardware to full extend). thanks 2012-08-11 05:15:38 +0200 answered a question Black Screen Could you provide more specific information? Which Version of Virtual Box did you install? Did you follow the procedure in the Online documentation Sage Appliance Doc? Is it really a black screen or do you have some text on it (e.g. you mention the prompt for login?) Is it possible that you use an older version which is server only? - In this case you access the sage notebook from the windows browser (localhost:8000) best regards Emil 2012-07-27 11:05:58 +0200 received badge ● Great Answer (source) 2012-07-26 02:56:05 +0200 commented answer I don't find my Sage files? Happy it worked ;-). The above procederes might be necessary if you you wan't to upgrade to a new virtual machine (without the built in upgrade mechanism of sage). 2012-07-25 13:11:43 +0200 received badge ● Good Answer (source) 2012-07-25 12:34:39 +0200 received badge ● Nice Answer (source) 2012-07-25 10:19:27 +0200 answered a question I don't find my Sage files? I am sorry I can not verify my answer myself at the moment, because I have no virtualbox installed and only a very limited internet connection which doesn't allow me to download it and test the sage ova file. I think your files are not stored in the ova file, but when you install the ova file, there is a folder created wich contains the virtual machine files in your windows user directory. This could be e.g. C:\Users\Your_name\VirtualBox\VMs\Sage_VM1 (again I have no Windows installed and cannot check this, but I am pretty sure) You can run different virtual machines, each one will have a seperate directory. Inside this directory there should be 2 files, the first (the small one) contains general control information like amount of ram, processor and network settings, basically everything you can modify in the virtualbox control gui. The other file is a virtual disk image (its usually large). This is basically the image of your virtual hard disk partition, it will contain fedora linux + sage and also your user data. What is the best method to copy the old files to the new virtual machine? I don't know. Maybe there is an easy one which I am not aware of, but all I can is to point out 2 different procedures which are not difficult but might be a bit overwhelming for somebody new to VM'S and Linux in general. 1. Method: Attach the old disk image to the new virtual machine Copy the old disk image into the folder of the new virtual machine (drag and drop in windows). In the Virtualbox control Menu you can add a new harddisk or partition to the New virtual machine (select the old file disk image). The sage vm now will have 2 hard disk partitions - the new one, from where you will boot your virtual machine, but also additionally the old image as a second virtual hard disk. Now you should be able to access the files of the old disk image from inside the new virtual machine. Since I am not familiar enough with the sage VMs and I don't know if there is a possibility to do this from a gui interface I just can give some hints how to achieve this from the command line. To go to the command line you will have to press Ctrl-F1. Then you probably will have to login as root to mount the old partition. So at login use "root/sage" for username/password (If this is the wrong password please look in the Sage Appliance online documentation. Create a mountpoint for the old disk image: mkdir /media/old Mount the old disk: mount /dev/sdb1 /media/old (some excurs: sd_letter_number, the letter stand for the number of the harddisk and the number stands for the number of the partition, so probably the old disk image will be sdb1. You can list all available harddisk ... 2012-07-19 21:41:54 +0200 received badge ● Nice Answer (source) 2012-07-19 18:17:33 +0200 answered a question how to delete files in virtualbox? Start the virtual machine and get to the command shell by pressing Ctrl-F1 like described here: Sage Appliance Online Docs Log into the virtual machine as user gui. The user account running the web browser is called gui with password sage. sagevm login: gui Password: sage  This login should bring you in the /home/gui directory. You can list the contents of that directory with the command (short for list) ls  remove (rm) files with the command rm filename  Probably you can delete files also from the gui interface of the vm, but the commandline version should work in any case. 2012-06-27 07:47:02 +0200 received badge ● Good Answer (source) 2012-06-22 15:11:41 +0200 received badge ● Nice Answer (source)