间隔中的根

Question

请帮我修一下线路！ “For..”行有效并打印不包含根的区间。我必须输出剩余的 间隔，其中包括根 。（我知道这些间隔应该是2）我尝试了 ! 但它有点不对:(

X = {-2, 6}
spx = {-2, -1.90577, -1.81153, -1.59327, -1.375, -1.35785, -1.3407,    -1.24655, -1.22941, -1.11811, -0.934054, -0.80167, -0.75, -0.625,-0.5, -0.25, -0.0981238, 0.303752, 0.651876, 0.94833, 1, 1.5, 1.75,2.11731, 2.5, 2.5625, 2.625, 3.3125, 3.75, 4, 4.00964, 4.01928,4.25964, 4.36731, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6}
spfw = {33.3632, 43.263, 51.6709, 55.5421, 57.1266, 57.2511, 57.3756,58.059, 58.0778, 58.1995,56.846,55.1903,54.5739,53.0828,51.1542,48.9959,48.0325,42.2533, 36.408,30.7952,30.1551,28.6446,23.138,19.4168,6.47053,5.90328,5.32951,-0.513959, -0.750527, -6.38895, -6.39157, -6.39418,-6.36456, -6.09357, -6.28599, -5.25369, -4.19539, -2.18625, -0.133803,2.90414, 6.171}
spfn = {33.3632, 40.2933, 46.5882, 51.9781, 55.5583, 55.5708, 55.5762, 55.4604, 55.4393, 55.0045, 530116, 51.1309, 50.4546, 48.1226, 45.6012, 43.402, 42.066, 37.5522, 32.6864, 28.1979, 28.0685,25.7067, 17.5943,13.5547, -2.97428, -3.21054, -3.36422, -5.05466, -5.1301, -6.4392,-6.76879, -6.48231, -7.20196, -7.00719, -7.53373, -6.00246, -4.41058,-2.8187, -1.16621, 2.35765, 6.04694}
For[i = 1, i < Length@spfn, i++,
If[((0 < spfn[[i]]) && (0 < spfn[[i + 1]])) || 
((spfw[[i]] < 0) && (spfw[[i + 1]] < 0)),
   Print["1) exist no roots on: {", spx[[i]], ";", spx[[i + 1]], "}"];
]]

Answer 1

你可以用 ! 否定你的整个逻辑表达式：

 If[! (((0 < spfn[[i]]) && (0 < spfn[[i + 1]])) ||
       ((spfw[[i]] < 0) && (spfw[[i + 1]] < 0))), 
    Print["1) exist some roots on: {", spx[[i]], ";", spx[[i + 1]], "}"]]

注意我添加了一组括号，以便否定适用于整个表达式

您可以交替使用第三个参数 If:

 If[((0 < spfn[[i]]) && (0 < spfn[[i + 1]])) || 
    ((spfw[[i]] < 0) && (spfw[[i + 1]] < 0)), 
   Print["1) exist no roots on: {", spx[[i]], ";", spx[[i + 1]], "}"],
   Print["2) exist  roots on: {", spx[[i]], ";", spx[[i + 1]], "}"]]

..一旦您学会使用 Mathematica 的面向对象编程方法：

 First /@ Select[ 
         Transpose[
        Partition[#, 2, 1] & /@ {spx, spfn, spfw}]  , 
      ! ((#[[2, 1]] > 0  && #[[2, 2]] > 0) || 
        (#[[3, 1]] < 0  && #[[3, 2]] < 0)) & ]

(* {{2.11731, 2.5}, {2.5, 2.5625}, {2.5625, 2.625}, {2.625, 3.3125}, {5.5, 5.75}} *)

间隔中的根

Roots in the intervals

wolfram-mathematica

intervals