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北京石油化工学院2026年研究生招生接收调剂公告
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di_la_ke

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[求助] 求助mathematica大神 已有1人参与

求大神,x1+x2+x3+x4+x5+x6+x7=8;x1到x8为[0,8]区间的整数,怎么求解该方程的解的个数啊

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cooooldog

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ส็็็

引用回帖:
3楼: Originally posted by di_la_ke at 2014-09-07 22:24:40
为啥是c15_6啊
...

如果对x1, x2,..., x8没有大小排列的特定要求,同一组解可以随意组合,得到如下

Length@Reduce[{x1 + x2 + x3 + x4 + x5 + x6 + x7 + x8 == 8, 0 <= x1 <= 8,
  0 <= x2 <= 8, 0 <= x3 <= 8, 0 <= x4 <= 8, 0 <= x5 <= 8,
  0 <= x6 <= 8, 0 <= x7 <= 8, 0 <= x8 <= 8}, {x1, x2, x3, x4, x5, x6,
  x7, x8}, Integers]

一共6435个解;

如果要求  0<=  x1<=x2<=x3<=...<=<=x8    <=8, 则
sol = Reduce[{x1 + x2 + x3 + x4 + x5 + x6 + x7 + x8 == 8,
    0 <= x1 <= x2 <=  x3 <= x4 <= x5 <= x6 <= x7 <=  x8 <= 8}, {x1,
    x2, x3, x4, x5, x6, x7, x8}, Integers]; Length@sol

只有22个解
sol//MatrixForm

(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==0&&x7==0&&x8==8)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==0&&x7==1&&x8==7)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==0&&x7==2&&x8==6)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==0&&x7==3&&x8==5)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==0&&x7==4&&x8==4)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==1&&x7==1&&x8==6)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==1&&x7==2&&x8==5)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==1&&x7==3&&x8==4)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==2&&x7==2&&x8==4)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==0&&x6==2&&x7==3&&x8==3)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==1&&x6==1&&x7==1&&x8==5)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==1&&x6==1&&x7==2&&x8==4)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==1&&x6==1&&x7==3&&x8==3)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==1&&x6==2&&x7==2&&x8==3)||(x1==0&&x2==0&&x3==0&&x4==0&&x5==2&&x6==2&&x7==2&&x8==2)||(x1==0&&x2==0&&x3==0&&x4==1&&x5==1&&x6==1&&x7==1&&x8==4)||(x1==0&&x2==0&&x3==0&&x4==1&&x5==1&&x6==1&&x7==2&&x8==3)||(x1==0&&x2==0&&x3==0&&x4==1&&x5==1&&x6==2&&x7==2&&x8==2)||(x1==0&&x2==0&&x3==1&&x4==1&&x5==1&&x6==1&&x7==1&&x8==3)||(x1==0&&x2==0&&x3==1&&x4==1&&x5==1&&x6==1&&x7==2&&x8==2)||(x1==0&&x2==1&&x3==1&&x4==1&&x5==1&&x6==1&&x7==1&&x8==2)||(x1==1&&x2==1&&x3==1&&x4==1&&x5==1&&x6==1&&x7==1&&x8==1)
ส็็็็็็็็็็็็็็็็็็็็
5楼2014-09-08 21:01:03
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amefd

铁杆木虫 (职业作家)

【答案】应助回帖

★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ...
感谢参与,应助指数 +1
di_la_ke: 金币+100, ★★★很有帮助 2014-09-07 22:27:44
C15_6, C是组合数。
不要用tica了,手算即可
PhD是人类的好朋友。
2楼2014-09-07 22:19:26
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di_la_ke

铁虫 (小有名气)

引用回帖:
2楼: Originally posted by amefd at 2014-09-07 22:19:26
C15_6, C是组合数。
不要用tica了,手算即可

为啥是c15_6啊

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3楼2014-09-07 22:24:40
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amefd

铁杆木虫 (职业作家)

引用回帖:
3楼: Originally posted by di_la_ke at 2014-09-07 22:24:40
为啥是c15_6啊
...

x1'+x2'+...+x7'=15, where x1~x7 are positive integers.
在15个苹果之间插6个板,第一块板之前的苹果个数是x1,以此类推——话说发现错了,应该是C14_6.
为什么是苹果呢?因为小学美术老师是这么教我的
PhD是人类的好朋友。
4楼2014-09-07 22:31:14
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