今天我进行坐标变换，rx是绕x轴旋转的函数，rz是绕z轴旋转的函数

rx(-90)

ans =

   1.000000000000000                   0                   0                   0
                   0   0.000000000000000   1.000000000000000                   0
                   0  -1.000000000000000   0.000000000000000                   0
                   0                   0                   0   1.000000000000000

 rz(theta1)
 
ans =
 
[ cos(theta1), -sin(theta1), 0, 0]
[ sin(theta1),  cos(theta1), 0, 0]
[           0,            0, 1, 0]
[           0,            0, 0, 1]

结果：

T12=rx(-90)*rz(theta2)

T12 =
 
[                                                     cos(theta2),                                                    -sin(theta2),                                                 0, 0]
[ (4967757600021511*sin(theta2))/81129638414606681695789005144064, (4967757600021511*cos(theta2))/81129638414606681695789005144064,                                                 1, 0]
[                                                    -sin(theta2),                                                    -cos(theta2), 4967757600021511/81129638414606681695789005144064, 0]
[                                                               0,                                                               0,                                                 0, 1]

莫名出现了：4967757600021511/81129638414606681695789005144064等较长数字。

原因是：rx(-90)进行运算结果保存为long的类型，在与符号运算时，四舍五入时产生的。

解决办法：

T12=[1 0 0 0;0 0 1 0;0 -1 0 0;0 0 0 1]*rz(theta2)
 
T12 =
 
[  cos(theta2), -sin(theta2), 0, 0]
[            0,            0, 1, 0]
[ -sin(theta2), -cos(theta2), 0, 0]
[            0,            0, 0, 1]

在数值运算里出现这种莫名长度数字的解决办法是：

format long

2/5

0.4

对矩阵：

format long

aa=double(aa)