C# Decimal Arithmetic
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How could going from decimal to double avoid a divide by zero? I would have spent significant resources in discovering how that could be.
decimal x = 1;
decimal y = 0;
decimal z = x / y; // --> DivideByZeroExceptiondouble x = 1;
double y = 0;
double z = x / y; // z === double.PositiveInfinityThe
doubletype complies with IEEE 754[^].
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
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Finished converting the U.S. Naval Observatory Astrometry software from c and doubles to c# and decimal. The only calculations the decimals couldn't handle were the speed of light in meters (overflow) and weak gravity calculation (divide by zero). In those cases, had to use intermediate doubles. So now you know. :-D
It was only in wine that he laid down no limit for himself, but he did not allow himself to be confused by it. ― Confucian Analects: Rules of Confucius about his food
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decimal x = 1;
decimal y = 0;
decimal z = x / y; // --> DivideByZeroExceptiondouble x = 1;
double y = 0;
double z = x / y; // z === double.PositiveInfinityThe
doubletype complies with IEEE 754[^].
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
As the decimal representation does not provide any bit pattern for infinities, the divide operator has no way of returning any 'decimal.PositiveInfinity' - it doesn't exist. Similarly, there is no representation of Not a Number (NaN). Some values can be represented in float/double but not in decimal; others can be represented in decimal but not in float/double. If you really want / need to handle infinities in decimal, you can define your own AugmentedDecimal struct that is a decimal plus the required flag bits for flagging the value as, say, positive / negative infinities or NaN. Then, a DivideByZeroException handler may set these flag bits appropriately. Of course you then have to define the operators for AugmentedDecimal to check the flag bits as appropriate before performing the operation. This is built into the float hardware. decimal is essentially done in software, even without these augmentations. So it is slow anyway. But if that is what you need, that is the price you have to pay. Then: My guess is that the tiny part of float/double handling software that handles infinities properly is a fraction of a percent. You don't get an exception here, but when you try to use the value as a normal number (because no exception has signaled to you the exceptional value), your program may do funny things. Tracing back to the division that caused the infinity may be non-trivial. If you do write code that properly and throughout handles infinities (i.e. within that fraction of a percent), then I am sure that you would have no problems writing a proper handler for the decimal DivideByZeroException as well.
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Why decimals instead of doubles though? Not trying to question the decision, I'd like to understand for myself.
My guess is one of two: Either, the application calls for the higher precision (almost 29 decimal digits for decimal, less than 17 decimal digits for double), but the numeric range is sufficiently large. This level of precision is rarely needed, except in some extreme scientific calculations. Or, the application calls for full control of roundoff errors, with exact value representation of e.g. decimal fractions, rather than a binary approximation. This is a common requirement in e.g. accounting systems. (An alternative to decimal is of course to use a long value to represent an integer number of millicents or whatever the required precision of the transactions. Using decimal will usually require fewer application code lines, as you can deal directly with the unscaled amounts.) When I explain programming to beginners (and also to some at intermediate level needing some correction...), I know from experience that for some, understanding the principal difference between int and float is difficult. So I rather call it 'counts' and 'measurements'. The price of an apple is not a measurement, it is a count of the pennies you have to pay. So we use an int - int is a synonym for a count. If you weigh that apple, you do not count the grams, or milligrams, or micrograms - you will not get a measurement exactly right. So we use a float - float is a synonym for a measurement value. Even if you claim that the weight of the apple is exactly 123.456 grams, it nevertheless is a measurement, calling for a float, not a count of milligrams. Making beginners understand the difference between a count and a measurement is far easier than to explain int and float. In that framework, I really would like to consider decimal as a "counting" value, with the extension that it lets us count not only Euros or dollars, but even cents and tenths of a cent. With BCD, this was very explicit at the representation level as well; with decimal, it is blurred. C# documentation classifies it as a 'floating point numeric type'. Yet, decimal is functionally like BCD values, rather than as measurement float / double. Also by implementation, it is a scaled integer (i.e. counting) value. I think using decimal for measurement values is an abuse. If you really need more than the 17 digits of a double, then you should go for one of the 'infinite precision' libraries provided for almost any language. (Writing one is not that difficult - I made one myself in my student days.) If you measure the dimension of the universe down
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If the divisor in theory, mathematically, "should have been" zero but isn't because of imprecision as floats are not 'real' numbers of unlimited precision, then the underlaying algorithm should indeed be closely inspected and investigated. If the avoidance of a divide by zero exception is an artifact of limited precision, then I am getting close to call that a faulty implementation of the algorithm. If, on the other hand, the divisor is from a mathematical point of view - really non-zero, but has been zeroed by some software or hardware algorithmic rules, then these rules should be reconsidered. It should never be tolerated that a small, non-zero divisor causes a divide-by-zero error. That is simply incorrect! If the divisor is "valid", yet so small that it should be equivalent to zero, then it must be handled as a value (like zero), not causing an exception. If it could be handled in float format, it should be handled similarlu in decimal format!
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They use it for space missions. I'm telling you the mechanics; you want to analyze the writer's minds. You're trying to argue there is "zero" gravity when in fact there is; "imprecision" helps maintain it. A decimal can hold 28-29 digits; if gravity is less than that, it's still not "zero".
It was only in wine that he laid down no limit for himself, but he did not allow himself to be confused by it. ― Confucian Analects: Rules of Confucius about his food
In clinical chemistry it is common for the concentration of an analyte to be reported as "< 0.10 mg/dl" when that is the sensitivity of the test. Sensitivity of a test is defined by the random analytical variation of the test in the absence of ANY analyte, i.e. the "noise" in the measurement. cf. Gaussian standard error of estimate. In this example, a "result" of 0.005 mg/dl is analytically indistinguishable from 0.00 mg/dl. The same issues of analytical precision apply to the extremes of floating point calculation.
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My guess is one of two: Either, the application calls for the higher precision (almost 29 decimal digits for decimal, less than 17 decimal digits for double), but the numeric range is sufficiently large. This level of precision is rarely needed, except in some extreme scientific calculations. Or, the application calls for full control of roundoff errors, with exact value representation of e.g. decimal fractions, rather than a binary approximation. This is a common requirement in e.g. accounting systems. (An alternative to decimal is of course to use a long value to represent an integer number of millicents or whatever the required precision of the transactions. Using decimal will usually require fewer application code lines, as you can deal directly with the unscaled amounts.) When I explain programming to beginners (and also to some at intermediate level needing some correction...), I know from experience that for some, understanding the principal difference between int and float is difficult. So I rather call it 'counts' and 'measurements'. The price of an apple is not a measurement, it is a count of the pennies you have to pay. So we use an int - int is a synonym for a count. If you weigh that apple, you do not count the grams, or milligrams, or micrograms - you will not get a measurement exactly right. So we use a float - float is a synonym for a measurement value. Even if you claim that the weight of the apple is exactly 123.456 grams, it nevertheless is a measurement, calling for a float, not a count of milligrams. Making beginners understand the difference between a count and a measurement is far easier than to explain int and float. In that framework, I really would like to consider decimal as a "counting" value, with the extension that it lets us count not only Euros or dollars, but even cents and tenths of a cent. With BCD, this was very explicit at the representation level as well; with decimal, it is blurred. C# documentation classifies it as a 'floating point numeric type'. Yet, decimal is functionally like BCD values, rather than as measurement float / double. Also by implementation, it is a scaled integer (i.e. counting) value. I think using decimal for measurement values is an abuse. If you really need more than the 17 digits of a double, then you should go for one of the 'infinite precision' libraries provided for almost any language. (Writing one is not that difficult - I made one myself in my student days.) If you measure the dimension of the universe down
Greetings May I inquire if the beginners should simply be informed that int's represent the integers and float's the real numbers? Kind Regards Cheerios
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Greetings May I inquire if the beginners should simply be informed that int's represent the integers and float's the real numbers? Kind Regards Cheerios
The problem is that lots of people consider a weight of 454 gram an integer numeric value, rather than a real, especially if they use a digital scale. If you ask "the man in the street" to explain "integer" and "real" numbers, you may be surprised by the (lack of) answers you get! (There is nothing 'un-real' about, say, 'five' :-)) You cannot expect beginners in programming to have a solid background in mathematics. (Almost) everyone have little problems distinguishing between counting and measuring. Well, that is my experience. YMMV.
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The problem in this case isn't an avoidance of a divide by zero, it's that the value is so close to zero that system.decimal can't handle the number and truncates it to zero. The wider dynamic range of system.double can handle it.
If your application really needs to handle (application) epsilons as non-zero, then you certainly have to choose a data format that allows you to handle epsilons. Maybe decimal isn't for you. Note that even double is guaranteed to handle you application's epsilons. The Double struct defines a Double.Epsilon which is the smallest epsilon that can be represented as a double. If your application needs to handle smaller values, like Double.Epsilon/2 or smaller, the value will end up as zero. Using double does not avoid the problem entirely, just moved the borderline somewhat. If you make a cost calculation suggesting a unit sales price of USD 2.5000000001, and the customer pays two and a half dollar, then your accounting application probably does not want to handle a balance due of USD 0.0000000001, but set it to zero. Now this certainly can be represented by a decimal, but your accounting system should round the sales price to the number of decimal places it finds relevant - the decimal struct provides such a Round method. Your application should be conscious about epsilons: If it needs to be treated as non-zero, you use float / double (crossing fingers for the application epsilon being no smaller than Double.Epsilon). If (application) epsilons have no relevance, you should zero them, e.g. using a Round function.
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Finished converting the U.S. Naval Observatory Astrometry software from c and doubles to c# and decimal. The only calculations the decimals couldn't handle were the speed of light in meters (overflow) and weak gravity calculation (divide by zero). In those cases, had to use intermediate doubles. So now you know. :-D
It was only in wine that he laid down no limit for himself, but he did not allow himself to be confused by it. ― Confucian Analects: Rules of Confucius about his food