MATLAB 指令窗中的help指令和lookfor指令

作者：未知信息来源:未知 2006-1-26

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2 指令窗中的 help 指令2。1 直接使用 help 获得指令的使用说明【例 2。1-1 】假如准确知道所要求助的主题词，或指令名称，那末使用 help 是获得在线帮助的最简单有效的途径。help logmLOGM Matrix logarithm。...

2.9.2 指令窗中的 help 指令

2.9.2.1 直接使用 help 获得指令的使用说明

【例 2.9.2 .1-1 】假如准确知道所要求助的主题词，或指令名称，那末使用 help 获得在线帮助的最简单有效的途径。本例演示：关于矩阵对数函数 logm 使用说明的在线求助。

help logm
LOGM Matrix logarithm.
L = LOGM(A) is the matrix logarithm of A, the inverse of EXPM(A). Complex results are produced if A has negative eigenvalues. A warning message is printed if the computed expm(L) is not close to A.

[L,esterr] = logm(A) does not print any warning message, but returns an estimate of the relative residual,norm(expm(L)-A)/norm(A).

If A is real symmetric or complex Hermitian, then so is LOGM(A).

Some matrices, like A = [0 1; 0 0], do not have any logarithms, real or complex, and LOGM cannot be expected to produce one.

See also EXPM, SQRTM, FUNM.

2.9.2.2 使用 help 指令进行分类搜索

【例 2.9.2 .2-1 】运行不带任何限定的 help ，可以得到分类名称明细表。

help
HELP topics:
matlab\general - General purpose commands.
matlab\ops - Operators and special characters.
matlab\lang - Programming language constructs.
matlab\elmat - Elementary matrices and matrix manipulation.
matlab\elfun - Elementary math functions.
matlab\specfun - Specialized math functions.
...... ......
For more help on directory/topic, type "help topic".

2.9.2.3 采用 help topic 指令形式获得具体子类的指令明细

【例 2.9.2 .3-1 】如果用户想知道有关矩阵操作指令一栏表，那末就运行以下指令。

help elmat
Elementary matrices and matrix manipulation.
Elementary matrices.
zeros - Zeros array.
ones - Ones array.
...... ......

Basic array information.
size - Size of matrix.
length - Length of vector.
...... ......

Matrix manipulation.
reshape - Change size.
diag - Diagonal matrices and diagonals of matrix.
...... ......

Special variables and constants.
ans - Most recent answer.
eps - Floating point relative accuracy.
...... ......

Specialized matrices.
compan - Companion matrix.
gallery - Higham test matrices.
...... ......

〖说明〗省略号由笔者所加，用来表示被删除的内容。样做是出于节省篇幅的考虑。

2.9.3 指令窗中的 lookfor 指令

【例 2.9.3 -1 】查找包含积分这个关键词的所有指令。

lookfor integral
ELLIPKE Complete elliptic integral.
EXPINT Exponential integral function.
DBLQUAD Numerically evaluate double integral.
INNERLP Used with DBLQUAD to evaluate inner loop of integral.
QUAD Numerically evaluate integral, low order method.
QUAD8 Numerically evaluate integral, higher order method.
COSINT Cosine integral function.
SININT Sine integral function.
ASSEMA Assembles area integral contributions in a PDE problem.
COSINT Cosine integral function.
FOURIER Fourier integral transform.
IFOURIER Inverse Fourier integral transform.
SININT Sine integral function.

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