Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror
×

Comment ccomparison of C and CAS (Score 2, Insightful) 491

Computer algebra systems are high level programming language. Writing good code does not need
documentation.  The code itself shows what is done. Here is an example which takes two pictures
and procuces a GIF movie interpolating them:

A=Import["image1.jpg"]; B=Import["image2.jpg"];
width=Length[A[[1,1]]]; height=Length[A[[1]]];
ImageInterpolate[t_]:=Image[(t A[[1]]+B[[1]] (1-t)),Byte,ColorSpace->RGB,ImageSize->{width,height}];
Export["mix.gif",Table[ImageInterpolate[k/50],{k,0,50}],"GIF"]

It takes over a minute to process. A simple C program doing the same is a multiple times larger but also
needs multiple less time to process. But it needs to be documented because even simple things like
reading in a picture

  fgets(buffer,1025,in);
  if(strncmp(buffer,"P6",2)){
    fprintf(stderr,"Unsupported file format (need PPM raw)\n");
    exit(1);
  }

  do fgets(buffer,1025,in); while(*buffer == '#');     // get picture dimension
  x_size = atoi(strtok(buffer," "));
  y_size = atoi(strtok(NULL," "));
  fgets(buffer,1025,in);                               // get color map size
  c_size = atoi(buffer);

  if((image = (char *) malloc(3*x_size*y_size*sizeof(char)))==NULL){
    fprintf(stderr,"Memory allocation error while loading picture\n");
    exit(1);
  }

  i = 0;
  ptr = image;
  while(!feof(in) && i<3*x_size*y_size){ *ptr++ = fgetc(in); i++;}
  fclose(in);

But C it is worth the effort. For more advanced image manipulation tasks for example,
Mathematica often can no more be used,  due to memory or just because it takes too long
(Math link does not help here very much since objects like a movie (a vector of images) can just
not be fed into computer algebra systems without getting into memory problems, which deals with a movie as a whole).
For computer vision stuff for example, one needs to deal with large chunks of the entire movie).
While the simplicity of programming with high level programming languages is compelling, speed often matters.

There is an other nice benefit of a simple language like C: the code will work in 20 years. Computer algebra
systems evolve very fast and much what is done today does not work tomorrow any more in a new version. Higher
level languages evolve also faster. And large junks of internal CAS code are a "black box" invisible for the
user. Both worlds makes sense: the low level primitive, transparent and fast low level language and the slower, but
extremely elegant high level language.

Comment the formula which distroyed wall street (Score 3, Interesting) 198

Mathematical models always only work in a certain range As Newtonian mechanics well for smaller velocities and macroscopic bodies it has to be replaced for large velocities or in smaller scales. Exponential growth laws have to be replaced by logistic growth. etc Models are especially popular in probability theory. The text mentions Gaussian Copula function, the "rocket fuel" for collateralized debt obligation, which is cited as one of the reasons for the finance disaster. See "The formula that killed Wall street".

Comment breaking a lance (Score 1) 1134

An innovative company probably needs both: quirky people with unconventional work habits but who have ideas and can break a lance. If they are not particularly good at documenting things, it should be easy to have this done by others who are good at learning, absorbing, cleaning and improving a good idea.
Space

Gravitational Waves May Have Been Detected In 1987 221

KentuckyFC writes "In 1987, a physicist called Joe Weber claimed to have detected gravitational waves at the same time that other scientists spotted a supernova called SN1987A. His claims were largely ignored because of calculations showing that gravitational waves could not be strong enough to be picked up by Weber's equipment, a set of giant aluminium cylinders designed to vibrate as the waves passed by. But these calculations were based on first order effects in the way spacetime can be distorted. Now a new analysis shows that second order effects can enhance gravitational waves by four orders of magnitude, but only when certain asymmetries are present. It turns out that SN1987A possesses just the right kind of asymmetries to make this enhancement possible because the supernova wasn't entirely spherical. Which means that Weber, who died in 2000, may have been the first to see gravitational waves after all."
Cellphones

Amazon Releases iPhone Kindle Software 232

palmsolo writes "The Amazon Kindle 2 just started shipping last week, but Amazon surprised everyone late on March 3rd by placing the Amazon Kindle software for the iPhone in the Apple App Store. With the Whispersync technology you can now keep your Kindle and iPhone ebooks in sync and read everywhere you go. Readers on the iPhone also now get access to over 200,000 ebook titles on the Amazon Kindle storefront. Check out the hands-on image gallery and video of the Amazon Kindle software on the iPhone and Kindle 2."

Comment origin of urban myth (Score 5, Informative) 625

The source of the claim seems Gutmann's 1996 article: http://www.usenix.org/publications/library/proceedings/sec96/full_papers/gutmann/index.html where he says: "Data overwritten once or twice may be recovered by subtracting what is expected to be read from a storage location from what is actually read. Data which is overwritten an arbitrarily large number of times can still be recovered provided that the new data isn't written to the same location as the original data (for magnetic media), or that the recovery attempt is carried out fairly soon after the new data was written (for RAM)." It was challenged already in 2003 http://www.nber.org/sys-admin/overwritten-data-guttman.html where Feenberg writes: "Surveying all the references, I conclude that Gutmann's claim belongs in the category of urban legend." As usual, this story shows that individual claims have to be checked by independent parties. Even the claim that it can not be done.

Comment military level software (Score 1) 270

I would have expected that on a military level, all software and operating systems used should be compiled from source, the source checked and risky features locked down. That would exclude proprietary operating systems like windows and mac OX and even prepackaged open source systems. Its probably not cheaper but cases like this should be wake up calls.

Comment stewarts "letters to a mathematician" (Score 3, Informative) 564

A degree in math opens the door to many other areas: computer science, any other science, teaching or management. It essentially provides the flexibility and ability to think abstractly. Doing mathematical research is only one option, the actual work can be very applied. A good math education teaches naturally how to understand a complex issue, reduce it to a model which can be solved. Starting with "hard science" makes other areas easier to understand. A good reading for a student pondering the question whether math is an option is Ian Stewart's book "Letters to a young Mathematician".

Comment confidentiality (Score 1) 336

The question is not so much functionality or reliability. This will eventually converge. The main difference is confidentiality. Are the data on google docs treated correctly? Is it possible to access them for other purposes? It is convenient for example for schools to collect grades on a google spreadsheet. Are these data kept away from third eyes? Are students with good scores for example being targeted suddenly by job hunters? I'm not aware of any case, where data has leaked, but we put a lot of trust in companies offering online applications.
Robotics

Submission + - First Armed Robots on Patrol in Iraq

An anonymous reader writes: Robots have been roaming Iraq, since shortly after the war began. Now, for the first time — the first time in any warzone — the 'bots are carrying guns. The SWORDS robots, armed with M249 machine guns, "haven't fired their weapons yet," an Army official says. "But that'll be happening soon." The machines have actually been ready to a while, but safety concerns kept 'em off the battlefield. Now, the robots have kill switches, so "now we can kill the unit if it goes crazy," according to the Army. I feel safer already.

Slashdot Top Deals

<< WAIT >>

Working...