保留小数值的命令行计算器

Question

我刚刚找到了一个很好的命令行计算器程序bc并且对它很满意，直到我发现它对小数值进行四舍五入，从而导致精度损失。

根据其man页面：

所有数字在内部均以十进制表示，所有计算均以十进制完成。（此版本截断了除法和乘法运算的结果。）

您能否为 Ubuntu Maverick推荐一个等效的bc？我需要使用变量进行高级命令行计算。

Answer 1

您可以使用 设置小数部分的长度scale=n。

该命令echo 'scale=20;752/447' | bc产生：

1.68232662192393736017

请注意，即使数字符合比例，也可能会附加额外的零：

scale=20
1/2
.50000000000000000000

不幸的是，总是有一个舍入问题：

scale=50
1/3*3
.99999999999999999999999999999999999999999999999999

Answer 2

calc（我相信来自 package apcalc）的作用与 相同bc，但不圆。它的显示类似于bc，但与 不同bc，它理解科学记数法。例子：

> calc
C-style arbitrary precision calculator (version 2.12.3.3)
Calc is open software. For license details type:  help copyright
[Type "exit" to exit, or "help" for help.]

; a=234
; b=a/7
; b
    ~33.42857142857142857143
; c=b/1e20
; c
    ~0.00000000000000000033
; c*1e10
    ~0.00000000334285714286
; 

比较bc：

> bc -l
bc 1.06.95
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'. 
a=234
b=a/7
b
33.42857142857142857142
c=b/10^20
c
.00000000000000000033
c*1e10
(standard_in) 6: syntax error
c*10^10
.00000000330000000000

稍微搜索一下就会出现很多结果，并非所有结果都是相关的，但我相信一些试验会得到你想要的结果（例如 wcalc）：

aptitude search calc
i   apcalc                               - Arbitrary precision calculator (original name: calc)
i A apcalc-common                        - Arbitrary precision calculator (common files)
p   apcalc-dev                           - Library for arbitrary precision arithmetic
p   bandwidthcalc                        - file transfer time calculator written in GTK+
p   calcoo                               - Scientific calculator (GTK+)
p   calcurse                             - text-based calendar and todo manager
p   concalc                              - console calculator
p   extcalc                              - multifunctional scientific graphic calculator
p   gcalcli                              - Google Calendar Command Line Interface
i   gcalctool                            - GNOME desktop calculator
p   ipcalc                               - parameter calculator for IPv4 addresses
p   ipv6calc                             - small utility for manipulating IPv6 addresses
p   kcalc                                - calculator for KDE 4
p   keurocalc                            - universal currency converter and calculator - binary package
p   keurocalc-data                       - universal currency converter and calculator - data package
p   lcalc                                - a program for calculating with L-functions
p   libcolor-calc-perl                   - Perl module for simple calculations with RGB colors
p   libdate-calc-perl                    - Perl library for accessing dates
p   libdate-pcalc-perl                   - Perl module for Gregorian calendar date calculations
p   libmath-basecalc-perl                - Convert numbers between various bases
p   libmath-calc-units-perl              - Human-readable unit-aware calculator
p   libmath-calculus-differentiate-perl  - Algebraic Differentiation Engine
p   libmath-calculus-expression-perl     - Algebraic Calculus Tools Expression Class
p   libmath-calculus-newtonraphson-perl  - Algebraic Newton Raphson Implementation
p   libticalcs-dev                       - Texas Instruments calculator communication library [development files]
p   libticalcs2-7                        - Texas Instruments calculator communication library
p   libwww-google-calculator-perl        - Perl interface for Google calculator
p   octave-physicalconstants             - provide physical constants values in Octave
i   openoffice.org-calc                  - office productivity suite -- spreadsheet
v   openoffice.org2-calc                 -
p   python-ipcalc                        - perform IP subnet calculations
v   python2.6-ipcalc                     -
p   r-cran-epicalc                       - GNU R Epidemiological calculator
p   rpncalc                              - RPN calculator trying to emulate an HP28S
p   science-numericalcomputation         - Debian Science Numerical Computation packages
p   sipcalc                              - Advanced console-based ip subnet calculator
p   subnetcalc                           - IPv4/IPv6 Subnet Calculator
p   sugar-calculate-activity             - calculate activity for the Sugar graphical shell
p   tapecalc                             - a full-screen tape editor that lets the user edit a calculation
p   transcalc                            - microwave and RF transmission line calculator
p   wcalc                                - A flexible command-line scientific calculator
p   wmcalclock                           - A dock.app which simply tells time and date
p   xsmc-calc                            - Smith Chart calculator for X

Answer 3

我建议使用 Python 作为命令行计算器：

$ python
>>> from math import *
>>> help(sin)
    sin(x)

    Return the sine of x (measured in radians).

我也推荐 IPython 或 IDLE。两者都极大地提高了标准外壳的可用性。

更新：使用 python3 避免截断意外：

$ python2.7

>>> 10/3
3

$ python3

>>> 10/3
3.3333333333333335

Answer 4

在这个意义上你失去了精度：如果将精度设置为 10 位十进制数字，则除法将被截断为 10 位十进制数字，这是一个连贯的选择。

如果您要寻找精确的计算器，则需要一个符号系统，如maxima.

顺便说一下，bc支持变量。

Answer 5

“genius”是最先进的计算器，提供命令行和 GUI 选项。查看手册了解详细信息，并查看http://www.jirka.org/genius.html。

要安装，只需键入：

sudo apt-get install genius gnome-genius