# The LD LASSO function

### Description

This function implements a method for the automatic selection of parameters for the LD LASSO. It returns three solutions, the fused, cp-optimal, and unfused solutions. It also creates a matrix of solutions needed for creating the trace plot.

### Usage

1 2 | ```
ld_lasso_method(block.obj, block.cood = NA, Xa = NA, Y = NA, bpmap = NA,
maxcol = 5e3, p.frac = 0.10, B = 5, s2low = 5e-3, s2high = 5e1, s2.vec.length = 4, null = FALSE)
``` |

### Arguments

`block.obj` |
An object of class gwaa.data from GenABEL. |

`block.cood` |
A vector of length p+1, where p is the number of SNPs. block.cood is an indicator vector that indicates block boundaries at all p+1 SNP bounded intervals. Use find.bounds to create this vector. |

`Xa` |
If block.obj is NA then a genotype matrix must be provided. Xa is a matrix of genotype values codes as 0, 1 or 2 for homozygous major, heterozygous, or homozygous minor, respectively. |

`Y` |
If block.obj is NA then a phenotype vector Y must be provided. Y is a vector of diagnoses, where 0 is non-diseased and 1 is diseased. |

`bpmap` |
A vector of map positions in terms of kB from the left boundary |

`maxcol` |
The upper limit on the number of columns in the constraint matrix. This is to prevent computational overload. Increasing maxcol may increase computation time and memory needed. |

`p.frac` |
The fraction of SNPs allowed in LASSO model under null hypothesis. This parameter is used in the function get.s1. |

`B` |
The number of bootstrap iterations for cp estimate. |

`s2low` |
The lower limit of the s2 vector |

`s2high` |
The upper limit of the s2 vector |

`s2.vec.length` |
The number of exponentially spaced values of s2. |

`null` |
A logical variable that indicates if analysis should be performed on permuted phenotype vector. |

### Details

Use function find.bounds to create block.cood vector with MATILDE MCMC methods. See ldlasso help page for details on the package MATILDE.

### Value

`beta1` |
The ld lasso solution with s2 that minimizes cp (cp-optimal solution) |

`beta2` |
The ld lasso solution for lower limit of s2 interval (fused solution) |

`beta3` |
The ld lasso solution for upper limit of s2 interval (unfused solution) |

`s2star` |
The s2 value that minimizes cp |

`cp.obj` |
A list that contains information used for cp estimation |

`log10p` |
A vector of log10 p values for test of allelic association |

`bpmap` |
A vector of map positions in base pairs |

`block.bounds.vec` |
A vector of block boundaries in kB from left boundary |

`s1` |
the LASSO constraint |

`B` |
Number of bootstrap samples |

`s2.vec.length` |
The length of the s2 vector |

### Author(s)

Samuel G. Younkin

### References

Samuel Younkin, Joseph Nadeau, Robert Elston and J. Sunil Rao, "The Linkage Disequilibrium LASSO for SNP Selection in a Genetic Association Study of Late Onset Alzheimer Disease," Technical Report, 2010

### See Also

ld_lasso

### Examples

1 2 3 4 5 | ```
# Load example data
# data(ldlasso_example)
# Run the method with low B and s2.vec.length first to test.
# ldlasso.obj <- ld_lasso_method( block.obj, block.cood, B = 3, s2.vec.length = 2 )
``` |

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