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Sudoku!

This is one of my hobbies. I share with you becouse is a good way to distract you of stress from University or School! I hope you like it! Oh, I'll give to you a little advice: When you finish it, please go back to study numerical methods.
El sudoku del día por SudokusWeb.com

Sunday, May 09, 2010

*Accuracy and Precision



The errors associated with both calculations and measurements can be characterized with regard to their accuracy and precision. Accuracy refers to how closely a computer or measured value agrees with the true value. Precision refers to how closely individual computed or measured values agree with each other. These concepts can be illustrated graphically ussing an analogy from target practice. The bullet holes on each target in Figure can be thought of as the predictions of a numerical technique, whereas the bull's-eye represents the truth. Inaccuracy is defined as systematic deviation from the truth. Thus, although the shots in Fig. (3) are more tightly grouped than those in Fig. (1), the two cases are equally biased because they are both centered on the upper left quadrant of the target. Imprecision, on the other hand, refers to the magnitude of the scatter. Therefore, although Fig. (2) and (4) are equaly accurate (that is, centered on the bull's-eye), the later is more precise because the shots are tightly grouped. Numerical methods should be sufficiently accurate or unbiased to meet the requirements of a particular engineering problem. They also should be precise enough for adequate engineering desing.

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