midas gen提供三种特征值向量分析类型

实在是太着急了，急求高手解答，否则不会重发此贴
midas gen提供三种特征值向量分析类型：子空间迭代，Lanczos和多重Rith向量法，设计时该如何区分这三种方法，什么情况下选用哪种特征值分析类型呢，本人做一工程，出现如下错误：
MULTI-FRONTAL SOLVER
AVAILABLE MEMORY = 1384.6 MBYTES
ENTRY PHASE FOR RENUMBERING
ENTRY NUMBERING_EQN
ENTRY FORM_STIFF_MASS_LOAD
THE INDIVIDUAL ELEMENT STIFFNESS AND LOAD MATRICES WILL NOW BE FORMED.
ELEMENT NO. : 20707 OF 20707
ENTRY SOLUTION PHASE
ENTRY LOAD_BLOCK
TOTAL NUMBER OF VALID DOFS IN MODEL : 113868
ENTRY ASSM_STIFF_LOAD ( FORM GLOBAL EQUILIBRIUM EQUATIONS IN BLOCKS )

ENTRY STATIC ANALYSIS
MULTI-FRONTAL SOLUTION HAS BEEN COMPLETED.
DISPLACEMENT/FORCE/STRESS OUTPUT.
ELEM. : 20707 OF 20707

ENTRY EIGEN FOR RESPONSE SPECTRUM ANALYSIS
EIGEN SOLUTION : SUBSPACE ITERATION METHOD.
* SUBSPACE ITERATION NUMBER = 20

WARNING : MAXIMUM NUMBER OF ITERATION HAS BEEN REACHED
CHECK TOLERANCE IN THE RESULT TABLE
MODE SHAPE OUTPUT.
DISPLACEMENT/FORCE/STRESS OUTPUT FOR EACH MODE.
ELEM. : 20707 OF 20707
分析一下应该是特征值向量分析类型的问题，我是应该增大子空间迭代的步数，增大收敛误差还是将特征值向量分析类型改为多重Rith向量法，而多重Rith向量法有如何实现呢，恳请各位大侠不吝赐教